INCOME TAXES

Income tax expense was $15 million and $40 million for the three months ended March 31, 2018 and 2017, respectively. For the three months ended March 31, 2018, changes in the effective tax rate from the prior period include lower level of earnings, the reduction in U.S. tax rate from 35% to 21%, and related tax expense and tax planning strategies made available in the first quarter of 2018.

The following table summarizes the difference between income tax (benefit) expense at the U.S. statutory rate of 21% and 35%, respectively, and the income tax (benefit) expense at effective worldwide tax rates for the respective periods:



	Three Months Ended March 31,
Millions of dollars	2018			2017
Earnings before income taxes	$	109		$	198

Income tax expense computed at United States statutory tax rate	23			69
U.S. foreign income items, net of credits	(11		)	(19		)
Foreign government tax incentive	—			(2		)
Other	3			(8		)
Income tax expense computed at effective worldwide tax rates	$	15		$	40

At the end of each interim period, we make our best estimate of the effective tax rate expected to be applicable for the full fiscal year and the impact of discrete items, if any, and adjust the quarterly rate as necessary.

United States Government Tax Legislation

On December 22, 2017, H.R.1 (the “Tax Cuts and Jobs Act”) was signed into law. Significant provisions include the reduction in the U.S. federal corporate income tax rate from 35% to 21%, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates new taxes on certain foreign sourced earnings. We are applying the guidance in SAB 118 when accounting for the enactment-date effects of the Tax Cuts and Jobs Act. At March 31, 2018, we have not completed our accounting for all of the tax effects of the Tax Cuts and Jobs Act and did not recognize any significant impacts to the provisional amounts recognized as of December 31, 2017. We will continue to make and refine our calculations as additional analysis is completed. Our estimates may also be affected as we gain a more thorough understanding of the tax law and as interpretive guidance is issued by the U.S. government. These changes could have a material impact in future periods.