The 2005 acquisition of the Kaneb companies more than doubled NuStar's asset base to 9,300-plus miles of crude-oil and refined-product pipelines, 86 terminal facilities, and four crude-oil storage facilities. (Source: Morningstar)

Buckeye Partners (BPL) - Owns and operates refined petroleum pipelines and storage terminals in the United States. Most of the company's assets are found in the Northeast and Midwest, though it also operates terminals and some smaller pipelines in the Southeast and West. Buckeye's pipelines transport a variety of refined petroleum products connecting refineries, storage facilities, other companies' pipelines, and airports. (Source: Morningstar)

Boardwalk Pipeline Partners (BWP) - Was formed in August 2005 by its parent, Loews Corporation, to acquire and develop natural-gas pipelines and storage facilities. The partnership owns two interstate natural-gas pipeline systems, which consist of 13,470 miles of pipe spanning from Texas to Ohio, and 11 underground natural-gas storage facilities. Aggressive expansion plans will increase total pipeline and storage capacity dramatically during the next several years. (Source: Morningstar)

Energy Transfer Partners (ETP) - A master limited partnership primarily engaged in natural-gas transportation and storage. The partnership operates more than 12,000 miles of natural-gas gathering and intrastate transportation pipelines in Texas and Louisiana and the 2,500-mile Transwestern interstate pipeline. Also, Energy Transfer Partners is the third-largest retail marketer of propane in the U.S., serving more than a million customers in 41 states. (Source: Morningstar)

Unit Corporation (UNT) - Unit is engaged in the contract drilling of oil and natural-gas wells. The company also develops, acquires, and produces oil and natural-gas properties and markets natural gas. Unit operates primarily in the Texas Gulf coast and Rocky Mountain regions, as well as in the Anadarko and Arkoma Basins, which cover portions of Oklahoma, Texas, Kansas, and Arkansas. The company owns and operates approximately 75 drilling rigs in these regions. Unit is based in Tulsa, Oklahoma. (Source: Morningstar)

Ensco International (ESV) - Owns one of the newest jack-up fleets in the contract drilling industry, which drills for oil and natural gas globally. The firm has been acquiring jack-ups since the early 1990s and has recently expanded its 46-jack-up fleet with its first semisubmersible. It has several additional semisubmersibles under construction.