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 and discontinue or curtail the stock repurchase program 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 18, Short-Term Debt, on page 77.

Common Stock Repurchase Program In July 2010, the Board of Directors approved an ongoing stock repurchase program with no set term or monetary limits. From the inception of the program through the end of 2018, the company purchased 195.8 million shares for $21.75 billion, including 14.9 million shares for $1.75 billion in the second half 2018. On February 1, 2019, the company announced that the Board of Directors authorized a new stock repurchase program with a maximum dollar limit of $25 billion and no set term limits. Repurchases may be made from time to time in the open market, by block purchases, in privately negotiated transactions or in such other manner as determined by the company. The timing of the repurchases and the actual amount repurchased will depend on a variety of factors, including the market price of the company's shares, general market and economic conditions, and other factors. The stock repurchase program does not obligate the company to acquire any particular amount of common stock, and it may be suspended or discontinued at any time.

Capital and Exploratory Expenditures

Capital and exploratory expenditures by business segment for 2018, 2017 and 2016 are as follows:

Total expenditures for 2018 were $20.1 billion, including $5.7 billion for the company’s share of equity-affiliate expenditures, which did not require cash outlays by the company. In 2017 and 2016, expenditures were $18.8 billion and $22.4 billion, respectively, including the company’s share of affiliates’ expenditures of $4.7 billion and $3.8 billion, respectively.

Of the $20.1 billion of expenditures in 2018, 88 percent, or $17.7 billion, related to upstream activities. Approximately 87 percent was expended for upstream operations in 2017 and 90 percent in 2016. International upstream accounted for 60 percent of the worldwide upstream investment in 2018, 69 percent in 2017 and 77 percent in 2016.

The company estimates that 2019 capital and exploratory expenditures will be $20 billion, including $6.3 billion of spending by affiliates. This is in line with 2018 expenditures, and reflects a robust portfolio of upstream and downstream investments, highlighted by the company's Permian Basin position, and additional shale and tight development in other basins. Approximately 87 percent of the total, or $17.3 billion, is budgeted for exploration and production activities. Approximately $10.4 billion of planned upstream capital spending relates to base producing assets, including $3.6 billion for the Permian and $1.6 billion for other shale and tight rock investments. Approximately $5.1 billion of the upstream program is planned for major capital projects