diff --git a/src/main/kotlin/com/frankenergie/smartasset/controller/OrderUpdateController.kt b/src/main/kotlin/com/frankenergie/smartasset/controller/OrderUpdateController.kt
index dd93385..9f9ca72 100644
--- a/src/main/kotlin/com/frankenergie/smartasset/controller/OrderUpdateController.kt
+++ b/src/main/kotlin/com/frankenergie/smartasset/controller/OrderUpdateController.kt
@@ -2,8 +2,11 @@ package com.frankenergie.smartasset.controller
 
 import com.frankenergie.smartasset.model.OrderUpdateRequest
 import com.frankenergie.smartasset.model.OrderUpdateResponse
+import com.frankenergie.smartasset.model.PurchaseSummary
 import com.frankenergie.smartasset.service.OrderBookService
+import com.frankenergie.smartasset.service.PurchaseTrackerService
 import org.springframework.http.ResponseEntity
+import org.springframework.web.bind.annotation.GetMapping
 import org.springframework.web.bind.annotation.PostMapping
 import org.springframework.web.bind.annotation.RequestBody
 import org.springframework.web.bind.annotation.RequestMapping
@@ -11,11 +14,20 @@ import org.springframework.web.bind.annotation.RestController
 
 @RestController
 @RequestMapping("/api")
-class OrderUpdateController(private val orderBookService: OrderBookService) {
+class OrderUpdateController(
+    private val orderBookService: OrderBookService,
+    private val purchaseTrackerService: PurchaseTrackerService
+) {
 
     @PostMapping("/orderupdate")
     fun orderUpdate(@RequestBody request: OrderUpdateRequest): ResponseEntity<OrderUpdateResponse> {
         val response = orderBookService.processOrder(request)
         return ResponseEntity.ok(response)
     }
+
+    @GetMapping("/purchases/average")
+    fun getPurchaseAverage(): ResponseEntity<PurchaseSummary> {
+        val summary = purchaseTrackerService.getSummary()
+        return ResponseEntity.ok(summary)
+    }
 }
diff --git a/src/main/kotlin/com/frankenergie/smartasset/model/ExecutedPurchase.kt b/src/main/kotlin/com/frankenergie/smartasset/model/ExecutedPurchase.kt
new file mode 100644
index 0000000..22fc4d6
--- /dev/null
+++ b/src/main/kotlin/com/frankenergie/smartasset/model/ExecutedPurchase.kt
@@ -0,0 +1,16 @@
+package com.frankenergie.smartasset.model
+
+import java.math.BigDecimal
+import java.time.Instant
+import java.time.LocalDateTime
+
+data class ExecutedPurchase(
+    val groupId: String,
+    val deliveryStart: LocalDateTime,
+    val deliveryEnd: LocalDateTime,
+    val quantity: BigDecimal,
+    val pricePerMWh: BigDecimal,
+    val timestamp: Instant = Instant.now()
+) {
+    val totalCost: BigDecimal get() = quantity * pricePerMWh
+}
diff --git a/src/main/kotlin/com/frankenergie/smartasset/model/PurchaseSummary.kt b/src/main/kotlin/com/frankenergie/smartasset/model/PurchaseSummary.kt
new file mode 100644
index 0000000..f7883bf
--- /dev/null
+++ b/src/main/kotlin/com/frankenergie/smartasset/model/PurchaseSummary.kt
@@ -0,0 +1,10 @@
+package com.frankenergie.smartasset.model
+
+import com.fasterxml.jackson.annotation.JsonProperty
+import java.math.BigDecimal
+
+data class PurchaseSummary(
+    @JsonProperty("total_mwh") val totalMWh: BigDecimal,
+    @JsonProperty("total_cost") val totalCost: BigDecimal,
+    @JsonProperty("average_price_per_mwh") val averagePricePerMWh: BigDecimal
+)
diff --git a/src/main/kotlin/com/frankenergie/smartasset/service/PurchaseTrackerService.kt b/src/main/kotlin/com/frankenergie/smartasset/service/PurchaseTrackerService.kt
new file mode 100644
index 0000000..145bb01
--- /dev/null
+++ b/src/main/kotlin/com/frankenergie/smartasset/service/PurchaseTrackerService.kt
@@ -0,0 +1,37 @@
+package com.frankenergie.smartasset.service
+
+import com.frankenergie.smartasset.model.ExecutedPurchase
+import com.frankenergie.smartasset.model.PurchaseSummary
+import org.springframework.stereotype.Service
+import java.math.BigDecimal
+import java.math.RoundingMode
+import java.util.concurrent.ConcurrentLinkedQueue
+
+@Service
+class PurchaseTrackerService {
+
+    private val purchases: ConcurrentLinkedQueue<ExecutedPurchase> = ConcurrentLinkedQueue()
+
+    fun recordPurchase(purchase: ExecutedPurchase) {
+        purchases.add(purchase)
+    }
+
+    fun getAllPurchases(): List<ExecutedPurchase> = purchases.toList()
+
+    fun getSummary(): PurchaseSummary {
+        val allPurchases = purchases.toList()
+        val totalMWh = allPurchases.sumOf { it.quantity }
+        val totalCost = allPurchases.sumOf { it.totalCost }
+        val averagePrice = if (totalMWh > BigDecimal.ZERO) {
+            totalCost.divide(totalMWh, 2, RoundingMode.HALF_UP)
+        } else {
+            BigDecimal.ZERO
+        }
+
+        return PurchaseSummary(totalMWh, totalCost, averagePrice)
+    }
+
+    fun clear() {
+        purchases.clear()
+    }
+}
diff --git a/src/test/kotlin/com/frankenergie/smartasset/service/PurchaseTrackerServiceTest.kt b/src/test/kotlin/com/frankenergie/smartasset/service/PurchaseTrackerServiceTest.kt
new file mode 100644
index 0000000..07f14f3
--- /dev/null
+++ b/src/test/kotlin/com/frankenergie/smartasset/service/PurchaseTrackerServiceTest.kt
@@ -0,0 +1,129 @@
+package com.frankenergie.smartasset.service
+
+import com.frankenergie.smartasset.model.ExecutedPurchase
+import org.junit.jupiter.api.Assertions.*
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+import java.math.BigDecimal
+import java.time.LocalDateTime
+
+class PurchaseTrackerServiceTest {
+
+    private lateinit var tracker: PurchaseTrackerService
+
+    @BeforeEach
+    fun setUp() {
+        tracker = PurchaseTrackerService()
+    }
+
+    @Test
+    fun `getSummary returns zeros when no purchases`() {
+        val summary = tracker.getSummary()
+
+        assertEquals(BigDecimal.ZERO, summary.totalMWh)
+        assertEquals(BigDecimal.ZERO, summary.totalCost)
+        assertEquals(BigDecimal.ZERO, summary.averagePricePerMWh)
+    }
+
+    @Test
+    fun `getSummary calculates average price correctly`() {
+        tracker.recordPurchase(
+            ExecutedPurchase(
+                groupId = "A",
+                deliveryStart = LocalDateTime.of(2024, 1, 15, 10, 0),
+                deliveryEnd = LocalDateTime.of(2024, 1, 15, 10, 15),
+                quantity = BigDecimal("10"),
+                pricePerMWh = BigDecimal("50.00")
+            )
+        )
+        tracker.recordPurchase(
+            ExecutedPurchase(
+                groupId = "B",
+                deliveryStart = LocalDateTime.of(2024, 1, 15, 10, 15),
+                deliveryEnd = LocalDateTime.of(2024, 1, 15, 10, 30),
+                quantity = BigDecimal("10"),
+                pricePerMWh = BigDecimal("60.00")
+            )
+        )
+
+        val summary = tracker.getSummary()
+
+        assertEquals(BigDecimal("20"), summary.totalMWh)
+        assertEquals(BigDecimal("1100.00"), summary.totalCost)
+        assertEquals(BigDecimal("55.00"), summary.averagePricePerMWh)
+    }
+
+    @Test
+    fun `getSummary calculates weighted average correctly`() {
+        tracker.recordPurchase(
+            ExecutedPurchase(
+                groupId = "A",
+                deliveryStart = LocalDateTime.of(2024, 1, 15, 10, 0),
+                deliveryEnd = LocalDateTime.of(2024, 1, 15, 10, 15),
+                quantity = BigDecimal("5"),
+                pricePerMWh = BigDecimal("40.00")
+            )
+        )
+        tracker.recordPurchase(
+            ExecutedPurchase(
+                groupId = "A",
+                deliveryStart = LocalDateTime.of(2024, 1, 15, 10, 15),
+                deliveryEnd = LocalDateTime.of(2024, 1, 15, 10, 30),
+                quantity = BigDecimal("15"),
+                pricePerMWh = BigDecimal("60.00")
+            )
+        )
+
+        val summary = tracker.getSummary()
+
+        // 5 * 40 + 15 * 60 = 200 + 900 = 1100
+        // 1100 / 20 = 55
+        assertEquals(BigDecimal("20"), summary.totalMWh)
+        assertEquals(BigDecimal("1100.00"), summary.totalCost)
+        assertEquals(BigDecimal("55.00"), summary.averagePricePerMWh)
+    }
+
+    @Test
+    fun `getAllPurchases returns all recorded purchases`() {
+        tracker.recordPurchase(
+            ExecutedPurchase(
+                "A",
+                LocalDateTime.of(2024, 1, 15, 10, 0),
+                LocalDateTime.of(2024, 1, 15, 10, 15),
+                BigDecimal("10"),
+                BigDecimal("50.00")
+            )
+        )
+        tracker.recordPurchase(
+            ExecutedPurchase(
+                "B",
+                LocalDateTime.of(2024, 1, 15, 10, 15),
+                LocalDateTime.of(2024, 1, 15, 10, 30),
+                BigDecimal("5"),
+                BigDecimal("55.00")
+            )
+        )
+
+        val purchases = tracker.getAllPurchases()
+
+        assertEquals(2, purchases.size)
+    }
+
+    @Test
+    fun `clear removes all purchases`() {
+        tracker.recordPurchase(
+            ExecutedPurchase(
+                "A",
+                LocalDateTime.of(2024, 1, 15, 10, 0),
+                LocalDateTime.of(2024, 1, 15, 10, 15),
+                BigDecimal("10"),
+                BigDecimal("50.00")
+            )
+        )
+
+        tracker.clear()
+
+        assertTrue(tracker.getAllPurchases().isEmpty())
+        assertEquals(BigDecimal.ZERO, tracker.getSummary().totalMWh)
+    }
+}