* Acquires oilfield environmental company for $445 million * Will boost Gibson's U.S. presence * Raises dividend by 4 percent * Plans receipt offer to raise as much as C$403 mln CALGARY, Alberta, Oct 11 (Reuters) - Gibson Energy Inc , operator of the largest independent fleet of for-hire oil trucks in the United States, said on Thursday it has agreed to buy OMNI Energy Services Inc for $445 million to boost the size of its U.S. oilfield production and environmental services business. The Calgary, Alberta-based company also said it will raise its quarterly dividend by one Canadian cent to 26 Canadian cents and sell 15.84 million subscription receipts for C$22.10 each, for gross proceeds of C$350 million ($358.3 million), or as much as C$403 million should underwriters exercise an option to boost the offer size by 15 percent. Gibson said in a statement that OMNI's oilfield services operations are established in many of the fastest growing oil regions in the United States, such as North Dakota's Bakken oil-shale field, the Eagle Ford in Texas and the Tuscaloosa marine shale in Louisiana and Mississippi. The company said the acquisition brings new customers like Exxon Mobil Corp, Anadarko Petroleum Corp and others. "OMNI broadens Gibson's footprint in most of the major U.S. liquids focused basins (and) provides the scale we believe is required to grow the environmental services business in North America," Stewart Hanlon, Gibson's chief executive, said in a release. The privately held OMNI has its business by 30 percent per year since 2010. The Canadian company will add OMNI's 1,091 employees to its staff. The deal is expected to close by Oct. 31, Gibson said. The subscription receipt offering is co-led by BMO Capital Markets and RBC Capital Markets. Gibson shares were halted prior to the announcement. They last traded at C$22.74 on the Toronto Stock Exchange.