Mitsubishi Aircraft said Thursday it has signed a deal with US-based carrier SkyWest for 100 jets worth $4.2 billion, with an option to buy another 100 planes, in a \"major order\" for the Japanese firm. The Japanese company, founded in 2008, said it expected to deliver the first batch of planes from 2017 while the optional order could be delivered from 2021. The optional order could double the deal\'s value to over $8.0 billion based on its planes\' list price, Mitsubishi said, adding the pair\'s agreement would \"mutually position themselves for opportunities in the US regional airline industry\". SkyWest, one of the world\'s biggest regional airline operators, is partnered with major US carriers including Delta and United and serves nearly 170 destinations in the US, Canada, and Mexico. It flew about 24.5 million passengers last year. \"Without a doubt, this is a major order and significant boost for the MRJ (Mitsubishi Regional Jet) programme,\" Mitsubishi Aircraft chief Hideo Egawa said in a statement. Mitsubishi Aircraft, backed by several top Japanese firms including conglomerate Mitsubishi, automaker Toyota and trading giant Sumitomo, said this year it had reached a deal in principle with the US company for an order. \"SkyWest believes the MRJ with its significant advancements in fuel economy, passenger comfort and environmental friendliness, will be a valued addition to our fleet,\" it said in a statement. The Japanese firm\'s 70-90 seat regional jets are touted as having a next-generation design that is fuel-efficient and cuts down on noise. The company previously inked an order for 15 planes with Japan\'s All Nippon Airways and 50 jets from US-based Trans States Holdings. Last year it also announced a five-jet deal with Hong Kong-based aircraft leasing firm ANI Group Holdings. Worldwide demand for regional jets with 60 to 99 seats is expected to surge to more than 4,100 planes by 2031 from 1,810 units in 2011, according to research institute Japan Aircraft Development Corporation.