Statistics have been supplied by Thomson Reuters and are based on completed mergers, acquisitions, leveraged buyouts, tender offers, and privatizations.

The chart covers the biggest deals under $500 million, in which a U.S.-based company was involved as either the buyer or seller. All deals closed by June 29, 2012.

Western Gas Partners LP kicked off the year with its $483 million purchase of Mountain Gas Resources LLC and Monsanto Company (NYSE: MON) finished the first half with its $250 million acquisition of Precision Planting Inc.

For the full chart, click here.