diff --git a/CLAUDE.md b/CLAUDE.md
index 3ad40a9..f348461 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -12,6 +12,9 @@ depends only on the core modules it plugs into.
   `GraphQlCatalog/Model/ActiveFilters` keeps the filter of every products field by response key and
   turns it into a selection over the salable variants; `Plugin/Resolver/OptionsSelectionFollowsFilters`
   (sort order 20) hands core's resolver the uids. A uid the query passes wins for its attribute.
+- `GraphQlCatalogInventory`: `ProductInterface.stock_sources`, the source items of the enabled sources
+  of the website's stock in priority order, from MSI's services in one batch per request. The
+  quantity is physical: reservations count on the stock only.
 - `GraphQlCatalogSwatches`: the `swatch` field on aggregation, attribute and selected options.
   `Model/Resolver/SwatchData` reads the swatch under the key and builds the thumbnail URL of a
   stored image swatch; `Plugin/Output/*` and `Plugin/Layer/AggregationSwatches` fill the key from
diff --git a/README.md b/README.md
index f7bbc13..ce52a4c 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,7 @@ reads the frontend input and the swatches of a filter from the listing query.
 | `AttributeValueInterface.attribute`, `Aggregation.attribute` | `GraphQlCatalog` | The attribute metadata, as `customAttributeMetadataV2` returns it; null for a category aggregation |
 | `swatch` on `AggregationOptionInterface`, `CustomAttributeOptionInterface`, `AttributeSelectedOptionInterface` | `GraphQlCatalogSwatches` | The `SwatchDataInterface` of an option of a swatch attribute, or null |
 | `ConfigurableProduct.configurable_product_options_selection(followFilters)` | `GraphQlCatalogConfigurableProduct` | The selection the filter of the products query names: every super attribute the filter limits to one value, when a salable variant carries all of them |
+| `ProductInterface.stock_sources` | `GraphQlCatalogInventory` | The physical quantity, status, pickup flag and location per enabled source of the website's stock |
 
 The modules answer from core's resolvers and data providers and need nothing else.
 [GraphCommerce Catalog Storefront](https://github.com/graphcommerce-org/magento2-GraphCommerce_CatalogStorefront)
@@ -21,13 +22,13 @@ requires this package and serves the same fields from its documents.
 ```sh
 composer require graphcommerce/magento-graphql-catalog
 bin/magento module:enable GraphCommerce_GraphQlCatalog GraphCommerce_GraphQlCatalogSwatches \
-    GraphCommerce_GraphQlCatalogConfigurableProduct
+    GraphCommerce_GraphQlCatalogConfigurableProduct GraphCommerce_GraphQlCatalogInventory
 bin/magento setup:upgrade
 ```
 
 `GraphCommerce_GraphQlCatalogSwatches` needs Magento_SwatchesGraphQl and
-`GraphCommerce_GraphQlCatalogConfigurableProduct` needs Magento_ConfigurableProductGraphQl. A store
-without them leaves the module disabled.
+`GraphCommerce_GraphQlCatalogConfigurableProduct` needs Magento_ConfigurableProductGraphQl and
+`GraphCommerce_GraphQlCatalogInventory` needs MSI. A store without them leaves the module disabled.
 
 ## Modules
 
@@ -36,6 +37,7 @@ without them leaves the module disabled.
 | [`GraphQlCatalog`](src/GraphQlCatalog) | `custom_attributeV2`, the `attribute` of a value and an aggregation, the option swatch key |
 | [`GraphQlCatalogSwatches`](src/GraphQlCatalogSwatches) | The `swatch` fields from core's swatch helper |
 | [`GraphQlCatalogConfigurableProduct`](src/GraphQlCatalogConfigurableProduct) | `followFilters` on the configurable option selection |
+| [`GraphQlCatalogInventory`](src/GraphQlCatalogInventory) | `stock_sources` from MSI's source items |
 
 ## Extension point
 
diff --git a/composer.json b/composer.json
index 83c6fe3..e477ff7 100644
--- a/composer.json
+++ b/composer.json
@@ -1,6 +1,6 @@
 {
     "name": "graphcommerce/magento-graphql-catalog",
-    "description": "Catalog GraphQL fields for Magento 2 / Mage-OS: one custom attribute by code, the attribute metadata of a value and an aggregation, the swatch of every option, and a configurable option selection that follows the listing filter. One package with every module; each module directory is a package of its own for a subtree split.",
+    "description": "Catalog GraphQL fields for Magento 2 / Mage-OS: one custom attribute by code, the attribute metadata of a value and an aggregation, the swatch of every option, a configurable option selection that follows the listing filter, and the quantity per stock source. One package with every module; each module directory is a package of its own for a subtree split.",
     "type": "magento2-module",
     "license": "MIT",
     "require": {
@@ -14,22 +14,26 @@
     "replace": {
         "graphcommerce/module-graph-ql-catalog": "self.version",
         "graphcommerce/module-graph-ql-catalog-swatches": "self.version",
-        "graphcommerce/module-graph-ql-catalog-configurable-product": "self.version"
+        "graphcommerce/module-graph-ql-catalog-configurable-product": "self.version",
+        "graphcommerce/module-graph-ql-catalog-inventory": "self.version"
     },
     "suggest": {
         "magento/module-swatches-graph-ql": "GraphCommerce_GraphQlCatalogSwatches serves the swatch of an aggregation option, an attribute option and a selected option",
-        "magento/module-configurable-product-graph-ql": "GraphCommerce_GraphQlCatalogConfigurableProduct selects the configurable options the listing filter names"
+        "magento/module-configurable-product-graph-ql": "GraphCommerce_GraphQlCatalogConfigurableProduct selects the configurable options the listing filter names",
+        "magento/module-inventory-sales-api": "GraphCommerce_GraphQlCatalogInventory serves the quantity per source of the stock of the website"
     },
     "autoload": {
         "files": [
             "src/GraphQlCatalog/registration.php",
             "src/GraphQlCatalogSwatches/registration.php",
-            "src/GraphQlCatalogConfigurableProduct/registration.php"
+            "src/GraphQlCatalogConfigurableProduct/registration.php",
+            "src/GraphQlCatalogInventory/registration.php"
         ],
         "psr-4": {
             "GraphCommerce\\GraphQlCatalog\\": "src/GraphQlCatalog/",
             "GraphCommerce\\GraphQlCatalogSwatches\\": "src/GraphQlCatalogSwatches/",
-            "GraphCommerce\\GraphQlCatalogConfigurableProduct\\": "src/GraphQlCatalogConfigurableProduct/"
+            "GraphCommerce\\GraphQlCatalogConfigurableProduct\\": "src/GraphQlCatalogConfigurableProduct/",
+            "GraphCommerce\\GraphQlCatalogInventory\\": "src/GraphQlCatalogInventory/"
         }
     }
 }
diff --git a/dev/tests/bootstrap.php b/dev/tests/bootstrap.php
index 89ab1b9..c9a2fe0 100644
--- a/dev/tests/bootstrap.php
+++ b/dev/tests/bootstrap.php
@@ -20,3 +20,7 @@
 foreach ($package['autoload']['psr-4'] as $prefix => $path) {
     $loader->addPsr4($prefix, dirname(__DIR__, 2) . '/' . $path, true);
 }
+// The interface the DI compile generates: declared here with core's shape when no generated code exists.
+if (!interface_exists(\Magento\GraphQl\Model\Query\ContextExtensionInterface::class)) {
+    require __DIR__ . '/generated/ContextExtensionInterface.php';
+}
diff --git a/dev/tests/generated/ContextExtensionInterface.php b/dev/tests/generated/ContextExtensionInterface.php
new file mode 100644
index 0000000..ccc559c
--- /dev/null
+++ b/dev/tests/generated/ContextExtensionInterface.php
@@ -0,0 +1,17 @@
+<?php
+/**
+ * The extension interface Magento generates for the GraphQL context, for
+ * the unit tests of an installation without generated code.
+ */
+declare(strict_types=1);
+
+namespace Magento\GraphQl\Model\Query;
+
+interface ContextExtensionInterface extends \Magento\Framework\Api\ExtensionAttributesInterface
+{
+    /** @return \Magento\Store\Api\Data\StoreInterface|null */
+    public function getStore();
+
+    /** @param \Magento\Store\Api\Data\StoreInterface $store */
+    public function setStore(\Magento\Store\Api\Data\StoreInterface $store);
+}
diff --git a/src/GraphQlCatalogInventory/Model/Resolver/StockSources.php b/src/GraphQlCatalogInventory/Model/Resolver/StockSources.php
new file mode 100644
index 0000000..d4e446f
--- /dev/null
+++ b/src/GraphQlCatalogInventory/Model/Resolver/StockSources.php
@@ -0,0 +1,77 @@
+<?php
+declare(strict_types=1);
+
+namespace GraphCommerce\GraphQlCatalogInventory\Model\Resolver;
+
+use Magento\Framework\Api\SearchCriteriaBuilder;
+use Magento\Framework\GraphQl\Config\Element\Field;
+use Magento\Framework\GraphQl\Query\Resolver\BatchResolverInterface;
+use Magento\Framework\GraphQl\Query\Resolver\BatchResponse;
+use Magento\Framework\GraphQl\Query\Resolver\ContextInterface;
+use Magento\InventoryApi\Api\Data\SourceItemInterface;
+use Magento\InventoryApi\Api\GetSourcesAssignedToStockOrderedByPriorityInterface;
+use Magento\InventoryApi\Api\SourceItemRepositoryInterface;
+use Magento\InventorySalesApi\Model\StockByWebsiteIdResolverInterface;
+
+/**
+ * The source items of every product of the request in the enabled sources of the website's stock,
+ * read in one search.
+ */
+class StockSources implements BatchResolverInterface
+{
+    public function __construct(
+        private readonly StockByWebsiteIdResolverInterface $stockByWebsiteId,
+        private readonly GetSourcesAssignedToStockOrderedByPriorityInterface $sourcesOfStock,
+        private readonly SourceItemRepositoryInterface $sourceItemRepository,
+        private readonly SearchCriteriaBuilder $searchCriteriaBuilder,
+    ) {
+    }
+
+    public function resolve(ContextInterface $context, Field $field, array $requests): BatchResponse
+    {
+        $stockId = (int)$this->stockByWebsiteId->execute((int)$context->getExtensionAttributes()->getStore()->getWebsiteId())->getStockId();
+        $sources = [];
+        foreach ($this->sourcesOfStock->execute($stockId) as $source) {
+            if ($source->isEnabled()) {
+                $sources[$source->getSourceCode()] = $source;
+            }
+        }
+        $skus = array_values(array_unique(array_map(static fn($request) => (string)$request->getValue()['model']->getSku(), $requests)));
+        $items = [];
+        if ($sources && $skus) {
+            $criteria = $this->searchCriteriaBuilder
+                ->addFilter(SourceItemInterface::SKU, $skus, 'in')
+                ->addFilter(SourceItemInterface::SOURCE_CODE, array_keys($sources), 'in')
+                ->create();
+            foreach ($this->sourceItemRepository->getList($criteria)->getItems() as $item) {
+                $items[$item->getSku()][$item->getSourceCode()] = $item;
+            }
+        }
+        $response = new BatchResponse();
+        foreach ($requests as $request) {
+            $productItems = $items[(string)$request->getValue()['model']->getSku()] ?? [];
+            $rows = [];
+            foreach ($sources as $code => $source) {
+                if (!isset($productItems[$code])) {
+                    continue;
+                }
+                $extension = $source->getExtensionAttributes();
+                $rows[] = [
+                    'source_code' => $code,
+                    'name' => (string)$source->getName(),
+                    'quantity' => (float)$productItems[$code]->getQuantity(),
+                    'in_stock' => (int)$productItems[$code]->getStatus() === SourceItemInterface::STATUS_IN_STOCK,
+                    'is_pickup_location' => $extension && method_exists($extension, 'getIsPickupLocationActive') && $extension->getIsPickupLocationActive(),
+                    'latitude' => $source->getLatitude() === null ? null : (float)$source->getLatitude(),
+                    'longitude' => $source->getLongitude() === null ? null : (float)$source->getLongitude(),
+                    'postcode' => $source->getPostcode(),
+                    'city' => $source->getCity(),
+                    'country_code' => $source->getCountryId(),
+                ];
+            }
+            $response->addResponse($request, $rows);
+        }
+
+        return $response;
+    }
+}
diff --git a/src/GraphQlCatalogInventory/README.md b/src/GraphQlCatalogInventory/README.md
new file mode 100644
index 0000000..492d159
--- /dev/null
+++ b/src/GraphQlCatalogInventory/README.md
@@ -0,0 +1,10 @@
+# GraphCommerce_GraphQlCatalogInventory
+
+`ProductInterface.stock_sources`: the source items of the product in the enabled sources of the
+stock of the website, in source priority order, with the source name, the physical quantity, the
+source item status, the in-store pickup flag and the location. Reservations count on the stock
+only, so `quantity` is the physical quantity, not the salable quantity. A product without source
+items, such as a configurable product, answers an empty list.
+
+[`Model/Resolver/StockSources`](Model/Resolver/StockSources.php) is a batch resolver: one source
+item search for every product of the request.
diff --git a/src/GraphQlCatalogInventory/Test/Unit/Model/Resolver/StockSourcesTest.php b/src/GraphQlCatalogInventory/Test/Unit/Model/Resolver/StockSourcesTest.php
new file mode 100644
index 0000000..b0a887d
--- /dev/null
+++ b/src/GraphQlCatalogInventory/Test/Unit/Model/Resolver/StockSourcesTest.php
@@ -0,0 +1,91 @@
+<?php
+declare(strict_types=1);
+
+namespace GraphCommerce\GraphQlCatalogInventory\Test\Unit\Model\Resolver;
+
+use GraphCommerce\GraphQlCatalogInventory\Model\Resolver\StockSources;
+use Magento\Catalog\Model\Product;
+use Magento\Framework\Api\SearchCriteria;
+use Magento\Framework\Api\SearchCriteriaBuilder;
+use Magento\Framework\GraphQl\Config\Element\Field;
+use Magento\Framework\GraphQl\Query\Resolver\BatchRequestItemInterface;
+use Magento\GraphQl\Model\Query\ContextInterface;
+use Magento\GraphQl\Model\Query\ContextExtensionInterface;
+use Magento\InventoryApi\Api\Data\SourceInterface;
+use Magento\InventoryApi\Api\Data\SourceItemInterface;
+use Magento\InventoryApi\Api\Data\SourceItemSearchResultsInterface;
+use Magento\InventoryApi\Api\Data\StockInterface;
+use Magento\InventoryApi\Api\GetSourcesAssignedToStockOrderedByPriorityInterface;
+use Magento\InventoryApi\Api\SourceItemRepositoryInterface;
+use Magento\InventorySalesApi\Model\StockByWebsiteIdResolverInterface;
+use Magento\Store\Api\Data\StoreInterface;
+use PHPUnit\Framework\TestCase;
+
+class StockSourcesTest extends TestCase
+{
+    public function testTheItemsOfTheEnabledSourcesInPriorityOrder(): void
+    {
+        $stock = $this->createStub(StockInterface::class);
+        $stock->method('getStockId')->willReturn(2);
+        $stockByWebsite = $this->createMock(StockByWebsiteIdResolverInterface::class);
+        $stockByWebsite->expects(self::once())->method('execute')->with(3)->willReturn($stock);
+        $sources = $this->createStub(GetSourcesAssignedToStockOrderedByPriorityInterface::class);
+        $sources->method('execute')->willReturn([$this->source('shop', true), $this->source('closed', false), $this->source('warehouse', true)]);
+        $results = $this->createStub(SourceItemSearchResultsInterface::class);
+        $results->method('getItems')->willReturn([$this->item('A', 'warehouse', 7, 1), $this->item('A', 'shop', 2, 0), $this->item('B', 'shop', 1, 1)]);
+        $repository = $this->createMock(SourceItemRepositoryInterface::class);
+        $repository->expects(self::once())->method('getList')->willReturn($results);
+        $criteria = $this->createStub(SearchCriteriaBuilder::class);
+        $criteria->method('addFilter')->willReturnSelf();
+        $criteria->method('create')->willReturn($this->createStub(SearchCriteria::class));
+
+        $requests = [$this->request('A'), $this->request('B'), $this->request('C')];
+        $response = (new StockSources($stockByWebsite, $sources, $repository, $criteria))->resolve($this->context(), $this->createStub(Field::class), $requests);
+
+        self::assertSame(['shop', 'warehouse'], array_column($response->findResponseFor($requests[0]), 'source_code'));
+        self::assertSame([2.0, 7.0], array_column($response->findResponseFor($requests[0]), 'quantity'));
+        self::assertSame([false, true], array_column($response->findResponseFor($requests[0]), 'in_stock'));
+        self::assertSame('Shop shop', $response->findResponseFor($requests[1])[0]['name']);
+        self::assertSame([], $response->findResponseFor($requests[2]));
+    }
+
+    private function source(string $code, bool $enabled): SourceInterface
+    {
+        $source = $this->createStub(SourceInterface::class);
+        $source->method('getSourceCode')->willReturn($code);
+        $source->method('isEnabled')->willReturn($enabled);
+        $source->method('getName')->willReturn('Shop ' . $code);
+        $source->method('getCountryId')->willReturn('NL');
+        return $source;
+    }
+
+    private function item(string $sku, string $source, float $quantity, int $status): SourceItemInterface
+    {
+        $item = $this->createStub(SourceItemInterface::class);
+        $item->method('getSku')->willReturn($sku);
+        $item->method('getSourceCode')->willReturn($source);
+        $item->method('getQuantity')->willReturn($quantity);
+        $item->method('getStatus')->willReturn($status);
+        return $item;
+    }
+
+    private function request(string $sku): BatchRequestItemInterface
+    {
+        $product = $this->createStub(Product::class);
+        $product->method('getSku')->willReturn($sku);
+        $request = $this->createStub(BatchRequestItemInterface::class);
+        $request->method('getValue')->willReturn(['model' => $product]);
+        return $request;
+    }
+
+    private function context(): ContextInterface
+    {
+        $store = $this->createStub(StoreInterface::class);
+        $store->method('getWebsiteId')->willReturn(3);
+        $extension = $this->createStub(ContextExtensionInterface::class);
+        $extension->method('getStore')->willReturn($store);
+        $context = $this->createStub(ContextInterface::class);
+        $context->method('getExtensionAttributes')->willReturn($extension);
+        return $context;
+    }
+}
diff --git a/src/GraphQlCatalogInventory/composer.json b/src/GraphQlCatalogInventory/composer.json
new file mode 100644
index 0000000..c51c117
--- /dev/null
+++ b/src/GraphQlCatalogInventory/composer.json
@@ -0,0 +1,21 @@
+{
+    "name": "graphcommerce/module-graph-ql-catalog-inventory",
+    "description": "The physical quantity of a product per source of the website's stock in the catalog GraphQL schema, for any Magento store with MSI",
+    "type": "magento2-module",
+    "license": "MIT",
+    "require": {
+        "php": "~8.1.0|~8.2.0|~8.3.0|~8.4.0",
+        "magento/framework": "*",
+        "magento/module-catalog-graph-ql": "*",
+        "magento/module-inventory-api": "*",
+        "magento/module-inventory-sales-api": "*"
+    },
+    "autoload": {
+        "files": [
+            "registration.php"
+        ],
+        "psr-4": {
+            "GraphCommerce\\GraphQlCatalogInventory\\": ""
+        }
+    }
+}
diff --git a/src/GraphQlCatalogInventory/etc/module.xml b/src/GraphQlCatalogInventory/etc/module.xml
new file mode 100644
index 0000000..b50f804
--- /dev/null
+++ b/src/GraphQlCatalogInventory/etc/module.xml
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
+    <module name="GraphCommerce_GraphQlCatalogInventory">
+        <sequence>
+            <module name="Magento_CatalogGraphQl"/>
+            <module name="Magento_InventoryApi"/>
+            <module name="Magento_InventorySalesApi"/>
+        </sequence>
+    </module>
+</config>
diff --git a/src/GraphQlCatalogInventory/etc/schema.graphqls b/src/GraphQlCatalogInventory/etc/schema.graphqls
new file mode 100644
index 0000000..6f7416e
--- /dev/null
+++ b/src/GraphQlCatalogInventory/etc/schema.graphqls
@@ -0,0 +1,16 @@
+interface ProductInterface {
+    stock_sources: [ProductStockSource!]! @doc(description: "The quantity of the product in each enabled source of the stock of the website, in source priority order.") @resolver(class: "GraphCommerce\\GraphQlCatalogInventory\\Model\\Resolver\\StockSources")
+}
+
+type ProductStockSource @doc(description: "The physical quantity of a product in one source. Reservations count on the stock only, so the quantity is not the salable quantity.") {
+    source_code: String!
+    name: String!
+    quantity: Float!
+    in_stock: Boolean! @doc(description: "The source item status.")
+    is_pickup_location: Boolean! @doc(description: "The source is an active in-store pickup location.")
+    latitude: Float
+    longitude: Float
+    postcode: String
+    city: String
+    country_code: String
+}
diff --git a/src/GraphQlCatalogInventory/registration.php b/src/GraphQlCatalogInventory/registration.php
new file mode 100644
index 0000000..e4e3ded
--- /dev/null
+++ b/src/GraphQlCatalogInventory/registration.php
@@ -0,0 +1,6 @@
+<?php
+declare(strict_types=1);
+
+use Magento\Framework\Component\ComponentRegistrar;
+
+ComponentRegistrar::register(ComponentRegistrar::MODULE, 'GraphCommerce_GraphQlCatalogInventory', __DIR__);