with the variety and complexity of the various tax laws, creates a level of uncertainty, and requires judgment when addressing the impact of complex tax issues. Our effective tax rate and the amount of tax expense are dependent upon various factors, including the following: the tax laws of the jurisdictions in which income is earned; the ability to realize deferred tax assets at certain international subsidiaries;negotiation and dispute resolution with taxing authorities in the U.S. and international jurisdictions; and changes in tax laws.

The provision for income taxes is computed using the asset and liability method under this method, deferred tax assets and liabilities are recognized currently based on the anticipated future tax consequences of changes in the temporary differences between the book and tax bases of assets and liabilities. This method includes an estimate of the future realization of tax benefits associated with tax losses. Deferred tax assets and liabilities are measured using the currently enacted tax rates that apply to taxable income in effect for the years in which those assets are expected to be realized or settled.

Income tax expense for 2018 was \$73.3 million on \$299.8 million of pretax income and for 2017 was \$67.2 million on \$200.3 million of pretax income. For 2018, the reduction of the statutory federal corporate income tax rate due to the enactment of the Tax Cuts and Jobs Act of 2017 (the “Tax Reform Act”), as well as the mix of income and losses among various jurisdictions, resulted in a net tax increase of\$18.7 million on pre­tax income of \$99.5 million. Additionally, there was an \$11.0 million year­over­year increase in tax expense related to changes in the measurement of uncertain tax positions, offset by decreases related to audit settlements and the expiration of the statute of limitations. Further, there was a year­over­year \$1.9 million increase in withholding tax expense. These year­over­year tax increases were offset by year­over­year decreases of \$5.1 million related to unremitted foreign earnings and \$1.2 million for other small tax expense items, along with, most significantly, a \$19.2 million decrease in the 2018 tax expense related to the net provisional tax benefit related to the Tax Reform Act. The net provisional tax benefit included tax benefits of \$72.0 million resulting from the revaluation of deferred tax assets and liabilities, which were partially offset by \$52.8 million of transition tax expense.

During 2018, there was a \$24.8 million net increase in valuation allowances. This increase was a result of a \$30.2 million increase to valuation allowances related to net operating losses and other deferred tax assets, as well as an increase of \$0.6 million in new valuation allowances. These increases were partially offset by a \$6.0 million decrease in valuation allowances due to currency translation.

The SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”) to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Reform Act. SAB 118 also provides for a measurement period that should not extend beyond one year from the Tax Reform Act enactment date. As of October 31, 2018, our accounting for the Tax Reform Act was provisional. However, in accordance with SAB 118, we have recorded a reasonable estimate for the following items: a tax benefit related to the revaluation of deferred tax assets and liabilities of \$72.0 million; and a provisional tax expense as a result of the accrual for the transition tax liability of \$52.8 million. As a result, the net provisional tax benefit recorded in our consolidated financial statements for the year ended October 31, 2018 was \$19.2 million. Adjustments to the provisional estimates will be recorded and disclosed prospectively during the measurement period and may differ from these provisional amounts, due to, among other matters, additional analyses, changes in interpretations and assumptions we have made, additional regulatory guidance that may be issued, and actions we may take as a result of the Tax Reform Act.

We analyze potential income tax liabilities related to uncertain tax positions in the United States and international jurisdictions. The analysis of potential income tax liabilities results in estimates of income tax liabilities recognized for uncertain tax positions following the guidance of ASC 740, “Income Taxes.” The estimation of potential tax liabilities related to uncertain tax positions involves significant judgment in evaluating the impact of uncertainties in the application of ASC 740 and complex tax laws. We periodically analyze both potential income tax liabilities and existing liabilities for uncertain tax positions resulting in both new reserves and adjustments to existing reserves in light of changing facts and circumstances. This includes the release of existing liabilities for uncertain tax positions based on the expiration of statutes of limitation. During 2018, recognition of uncertain tax positions increased primarily due to increases in unrecognized tax benefits related to prior years and the current year, offset by decreases related to lapse in statute of limitations; whereas in 2017, the uncertain tax positions decreased primarily due to audit and statute of limitations releases attributable to non­US jurisdictions.

The ultimate resolution of potential income tax liabilities may result in a payment that is materially different from our current estimates. If our estimates recognized under ASC 740 prove to be different than what is ultimately resolved, such resolution could have a material impact on our financial condition and results of operations. While predicting the final outcome or the timing of the resolution of any particular tax matter is subject to various risks and uncertainties, we believe that our tax accounts related to uncertain tax positions are appropriately stated.

Refer to Note 11 of the Notes to Consolidated Financial Statements included in Item 8 of this Form 10­K for further information.