on its high-quality debt ratings, the company believes that it has substantial borrowing capacity to meet unanticipated cash requirements. During extended periods of low prices for crude oil and natural gas and narrow margins for refined products and commodity chemicals, the company can also modify capital spending plans to provide flexibility to continue paying the common stock dividend and also remain committed to retaining the company’s high-quality debt ratings.

Committed Credit Facilities Information related to committed credit facilities is included in Note 19, Short-Term Debt, on page 78.

Common Stock Repurchase Program In July 2010, the Board of Directors approved an ongoing share repurchase program with no set term or monetary limits. The company did not acquire any shares under the program in 2017 or 2016. From the inception of the program through 2014, the company had purchased 180.9 million shares for $20.0 billion.

Capital and Exploratory Expenditures

Capital and exploratory expenditures by business segment for 2017, 2016 and 2015 are as follows:

Total expenditures for 2017 were $18.8 billion, including $4.7 billion for the company’s share of equity-affiliate expenditures, which did not require cash outlays by the company. In 2016 and 2015, expenditures were $22.4 billion and $34.0 billion, respectively, including the company’s share of affiliates’ expenditures of $3.8 billion and $3.4 billion, respectively.

Of the $18.8 billion of expenditures in 2017, 87 percent, or $16.4 billion, related to upstream activities. Approximately 90 percent was expended for upstream operations in 2016 and 92 percent in 2015. International upstream accounted for 69 percent of the worldwide upstream investment in 2017, 77 percent in 2016 and 76 percent in 2015.

The company estimates that 2018 capital and exploratory expenditures will be $18.3 billion, including $5.5 billion of spending by affiliates. This planned reduction, compared to 2017 expenditures, reflects project completions, improved efficiencies, and investment high-grading, including the full funding of the company's advantaged Permian Basin position. Approximately 86 percent of the total, or $15.8 billion, is budgeted for exploration and production activities. Approximately $8.7 billion of planned upstream capital spending relates to base producing assets, including $3.3 billion for the Permian and $1.0 billion for other shale and tight rock investments. Approximately $5.5 billion of the upstream program is planned for major capital projects underway, including $3.7 billion associated with the Future Growth and Wellhead Pressure Management Project at the Tengiz field in Kazakhstan. Global exploration funding is expected to be about $1.1 billion. Remaining upstream spend is budgeted for early stage projects supporting potential future developments. The company will continue to monitor crude oil market conditions and expects to further restrict capital outlays should oil price conditions deteriorate.

Worldwide downstream spending in 2018 is estimated to be $2.2 billion, with $1.4 billion estimated for projects in the United States.

Investments in technology companies and other