| Tax effects of temporary differences for: | 2013 | 2012 | |||
| (millions of dollars) | |||||
| Property, plant and equipment | 50,884 | 48,720 | |||
| Other liabilities | 3,474 | 3,680 | |||
| Total deferred tax liabilities | 54,358 | 52,400 | |||
| Pension and other postretirement benefits | (6,573) | (8,041) | |||
| Asset retirement obligations | (6,083) | (5,826) | |||
| Tax loss carryforwards | (3,393) | (2,989) | |||
| Other assets | (6,246) | (6,135) | |||
| Total deferred tax assets | (22,295) | (22,991) | |||
| Asset valuation allowances | 2,491 | 1,615 | |||
| Net deferred tax liabilities | 34,554 | 31,024 | |||