higher between comparative periods, primarily due to higher margins at CPChem.

Refer to Note 12, beginning on page FS-37, for a discussion of Chevron’s investments in affiliated companies.

Other income of $1.2 billion in 2013 included net gains from asset sales of $710 million before-tax. Other income in 2012 and 2011 included net gains from asset sales of $4.2 billion and $1.5 billion before-tax, respectively. Interest income was approximately $136 million in 2013, $166 million in 2012 and $145 million in 2011. Foreign currency effects increased other income by $103 million in 2013, while decreasing other income by $207 million in 2012 and increasing other income by $103 million in 2011.

Crude oil and product purchases of $134.7 billion were down in 2013 mainly due to lower prices for refined products and lower volumes for crude oil, partially offset by higher refined product volumes. Crude oil and product purchases in 2012 decreased by $9.2 billion from the prior year mainly due to the 2011 sale of the company’s refining and marketing assets in the United Kingdom and Ireland and lower natural gas prices.

Operating, selling, general and administrative expenses increased $1.8 billion between 2013 and 2012 due to higher employee compensation and benefits costs of $720 million, construction and maintenance expenses of $590 million, and professional services costs of $500 million.

Operating, selling, general and administrative expenses increased $900 million between 2012 and 2011 mainly due to higher contract labor and professional services of $590 million, and higher employee compensation and benefits of $280 million.

Exploration expenses in 2013 increased from 2012 mainly due to higher charges for well write-offs.

Exploration expenses in 2012 increased from 2011 mainly due to higher geological and geophysical costs and well write-offs.

The increase in 2013 from 2012 was mainly due to higher depreciation rates for certain oil and gas producing fields, higher upstream impairments and higher accretion expense, partially offset by lower production levels. The increase in 2012 from 2011 was mainly due to higher depreciation rates for certain oil and gas producing fields, partially offset by lower production levels.

Taxes other than on income increased in 2013 from 2012 mainly due to the consolidation of the 64 percent-owned Star Petroleum Refining Company, beginning June 2012, and higher consumer excise taxes in the United States. Taxes other than on income decreased in 2012 from 2011 primarily due to lower import duties in the United Kingdom reflecting the sale of the company’s refining and marketing assets in the United Kingdom and Ireland in 2011. Partially offsetting the decrease were excise taxes associated with consolidation of Star Petroleum Refining Company beginning June 2012.

Effective income tax rates were 40 percent in 2013, 43 percent in 2012 and 43 percent in 2011. The decrease in the effective tax rate between 2013 and 2012 was primarily due to a lower effective tax rate in international upstream operations. The lower international upstream effective tax rate was driven by a greater portion of equity income in 2013 than in