(a) Capital commitments
| US$'000 | 2018 | 2017 |
| Contracted but not provided for | ||
| - vessel acquisitions and vessel equipment contracts | 70,247 | 32,335 |
(b) Operating lease commitments
Accounting policy – Operating leases
Leases in which a significant portion of the risks and rewards of ownership are retained by the lessor are classified as operating leases.
Critical accounting estimates and judgements – Classification of leases
The Group classifies its leases into either finance leases or operating leases taking into account of the spirit, intention, and application of HKAS 17 “Leases”.
Management assesses the classification of leases by taking into account the market conditions at the inception of the lease, the period of the lease and the probability of exercising purchase options, if any, attached to the lease. For those leases that would not transfer ownership of the assets to the Group at the end of the lease term, and that it is not reasonably certain that the purchase options, if any, attached to the arrangements would be exercised, they are being treated as operating leases.
(i) The Group as the lessee – payments
The Group had future aggregate minimum lease payments under non-cancellable operating leases as follows:
| US$'000 | Vessels | Land and buildings | Total |
| At 31 December 2018 | |||
| Within one year | 153,999 | 2,261 | 156,260 |
| In the second to fifth year | 151,644 | 8,236 | 159,880 |
| After the fifth year | 11,502 | 408 | 11,910 |
| 317,145 | 10,905 | 328,050 | |
| At 31 December 2017 | |||
| Within one year | 135,808 | 2,420 | 138,228 |
| In the second to fifth year | 238,012 | 7,892 | 245,904 |
| After the fifth year | 22,643 | 470 | 23,113 |
| 396,463 | 10,782 | 407,245 |
The Group’s operating leases for vessels have terms ranging from less than 1 year to 10 years (2017: less than 1 year to 10 years). Certain of the leases have escalation clauses, renewal rights and purchase options.
Accounting policy – Operating leases: where the Group is the lessee
Payments made under operating leases (net of any incentives received from the lessor) are charged to the income statement on a straight-line basis over the lease periods.
(ii) The Group as the lessor – receipts
The Group had future aggregate minimum lease receipts under non-cancellable operating leases for vessels as follows:
| US$'000 | 2018 | 2017 |
| At 31 December 2018 | ||
| Within one year | 32,408 | 32,294 |
| In the second to fifth year | 38,253 | 47,579 |
| After the fifth year | 16,560 | 23,130 |
| 87,221 | 103,003 |
The Group’s operating leases have terms ranging from less than 1 year to 15 years and they mainly represent the receipts from two Post-Panamax vessels amounting to US$70.7 million (2017: US$86.6 million).
Accounting policy – Operating leases: where the Group
is the lessor
When the Group leases out assets under operating leases,
the assets are included in the balance sheet and, where
applicable, are depreciated in accordance with the Group’s
depreciation policies as set out in Note 6 Property, plant
and equipment. Revenue arising from assets leased out
under operating leases is recognised on a straight-line basis
over the lease periods.