Total capital expenditures were $149.2 billion in 2011, representing a 16% decrease from $178.3 billion in 2010. This decline was driven by lower property acquisition activity in 2011. Property acquisition costs were $12.1 billion (proved) and $30.8 billion (unproved) in 2011. This acquisition activity was significantly lower than 2010, which included several corporate acquisitions (ExxonMobil/ XTO Energy, Apache/Mariner Energy, Inc. and Denbury/Encore Acquisition Company). Occidental Petroleum was the leading purchaser of proved properties in 2011 ($3.2 billion) due to acquisitions in South Texas, California and the Permian and Williston Basins. Chevron was a leader in both proved ($1.2 billion) and unproved ($7.4 billion) property acquisition costs with its acquisition of Atlas Energy, Inc., along with other asset acquisitions in the Marcellus and Utica shale formations. Marathon Oil posted proved property acquisition costs of $1.8 billion and unproved property acquisition costs of $3.3 billion as a result of several transactions in the Eagle Ford shale formation. Exploration costs increased 40% from $15.5 billion in 2010 to $21.7 billion in 2011. Development costs were $84.4 billion in 2011 compared with $61.5 billion in 2010, a 37% increase.