High seas sale transaction value: actual last buyer contract price governs assessment; importer must prove chain of sales. The actual high seas sale contract price paid by the last buyer constitutes the transaction value under Rule 4 of the Customs Valuation Rules, 1988 when the immediate sale was intended as an export to the country of importation; notional additions of standard high seas charges are inappropriate. The importer must prove the chain of high seas sales by producing original invoice, sale contracts and details of service charges/commissions; if declared value is doubtful, the Department may reject it and apply sequential valuation methods.