diff --git a/sharding/collation.go b/sharding/collation.go
new file mode 100644
index 0000000000..93279e2eec
--- /dev/null
+++ b/sharding/collation.go
@@ -0,0 +1,47 @@
+package sharding
+
+import (
+	"math"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+)
+
+type Collation struct {
+	header       *CollationHeader
+	transactions []*types.Transaction
+}
+
+type CollationHeader struct {
+	shardID              *big.Int
+	expectedPeriodNumber *big.Int
+	periodStartPrevHash  *common.Hash
+	parentCollationHash  *common.Hash
+	txListRoot           *common.Hash
+	coinbase             *common.Address
+	postStateRoot        *common.Hash
+	receiptsRoot         *common.Hash
+	sig                  []byte
+}
+
+func (c *Collation) Header() *CollationHeader           { return c.header }
+func (c *Collation) Transactions() []*types.Transaction { return c.transactions }
+
+func (c *Collation) SetHeader(h *CollationHeader) { c.header = h }
+func (c *Collation) AddTransaction(tx *types.Transaction) {
+	// TODO: Check transaction does not exceed gas limit
+	c.transactions = append(c.transactions, tx)
+}
+
+func (c *Collation) GasUsed() *big.Int {
+	g := uint64(0)
+	for _, tx := range c.transactions {
+		if g > math.MaxUint64-(g+tx.Gas()) {
+			g = math.MaxUint64
+			break
+		}
+		g += tx.Gas()
+	}
+	return big.NewInt(0).SetUint64(g)
+}
diff --git a/sharding/collation_test.go b/sharding/collation_test.go
new file mode 100644
index 0000000000..686de049d4
--- /dev/null
+++ b/sharding/collation_test.go
@@ -0,0 +1,81 @@
+package sharding
+
+import (
+	"math"
+	"math/big"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+)
+
+func TestCollation_AddTransactions(t *testing.T) {
+	tests := []struct {
+		transactions []*types.Transaction
+	}{
+		{
+			transactions: []*types.Transaction{
+				makeTxWithGasLimit(0),
+				makeTxWithGasLimit(1),
+				makeTxWithGasLimit(2),
+				makeTxWithGasLimit(3),
+			},
+		}, {
+			transactions: []*types.Transaction{},
+		},
+	}
+
+	for _, tt := range tests {
+		c := &Collation{}
+		for _, tx := range tt.transactions {
+			c.AddTransaction(tx)
+		}
+		results := c.Transactions()
+		if len(results) != len(tt.transactions) {
+			t.Fatalf("Wrong number of transactions. want=%d. got=%d", len(tt.transactions), len(results))
+		}
+		for i, tx := range tt.transactions {
+			if results[i] != tx {
+				t.Fatalf("Mismatched transactions. wanted=%+v. got=%+v", tt.transactions, results)
+			}
+		}
+	}
+}
+
+func TestCollation_GasUsed(t *testing.T) {
+	tests := []struct {
+		transactions []*types.Transaction
+		gasUsed      *big.Int
+	}{
+		{
+			transactions: []*types.Transaction{
+				makeTxWithGasLimit(100),
+				makeTxWithGasLimit(100000),
+				makeTxWithGasLimit(899900),
+			},
+			gasUsed: big.NewInt(1000000),
+		}, {
+			transactions: []*types.Transaction{},
+			gasUsed:      big.NewInt(0),
+		},
+		{
+			transactions: []*types.Transaction{
+				makeTxWithGasLimit(math.MaxUint64),
+				makeTxWithGasLimit(9001),
+				makeTxWithGasLimit(math.MaxUint64),
+			},
+			gasUsed: big.NewInt(0).SetUint64(math.MaxUint64),
+		},
+	}
+
+	for _, tt := range tests {
+		got := (&Collation{transactions: tt.transactions}).GasUsed()
+		if tt.gasUsed.Cmp(got) != 0 {
+			t.Errorf("Returned unexpected gasUsed. Got=%v, wanted=%v", got, tt.gasUsed)
+		}
+	}
+}
+
+func makeTxWithGasLimit(gl uint64) *types.Transaction {
+	return types.NewTransaction(0 /*nonce*/, common.HexToAddress("0x0") /*to*/, nil /*amount*/, gl, nil /*gasPrice*/, nil /*data*/)
+}