| 2013 | 2012 | ||||
| (millions of dollars) | |||||
| Beginning balance | 11,973 | 10,578 | |||
| Accretion expense and other provisions | 785 | 709 | |||
| Reduction due to property sales | (97) | (176) | |||
| Payments made | (664) | (816) | |||
| Liabilities incurred | 603 | 163 | |||
| Foreign currency translation | (344) | 290 | |||
| Revisions | 732 | 1,225 | |||
| Ending balance | 12,988 | 11,973 | |||