Since the beginning of 2009, PE-backed companies have added on a total of 960 companies headquartered in the U.S., according to the PitchBook Platform. Add-on acquisitions increased from 372 completed add-ons in 2009 to 474 in 2010 and have continued at a solid pace in 2011 with 114 so far this year. Roughly a third of the add-ons targeted B2B Products and Services companies, a reflection of the strong overall PE investment activity in that industry. However, there has been a gradual shift from add-ons in the B2B industry to others in recent years as its percentage of total add-on activity dropped from 39% in 2009 to 36% in 2010 and to 29% in 2011 to date. In the last six months alone, the portfolio companies of 213 PE investors have completed add-ons. The investors with the most acquisitive portfolio companies include The Blackstone Group with 10 add-ons and GS Capital Partners, GTCR, Investcorp and Metalmark Capital with 5 each.