Mobile point of sale terminals will make up almost half of all POS terminals in service by 2019, according to US technology market intelligence company ABI Research.Several companies have entered the mPOS market or upgraded their offerings this year, creating a competitive market for devices and services.However, there is very little market research into the sector.Most mPOS vendors are targeting businesses "on the go", offering them a way of taking card payments away from their business premises.But ABI Research said mid-size merchants and large retailers were looking at mPOS to provide "new acceptance capabilities" and improve "in-store mobility".It predicted that there would be 51 million mPOS terminals in use around the world by 2019, making up 46 per cent of all point of sale terminals.The report said there was a question mark over the business viability of mPOS and uncertainty about which type of vendor was most likely to make a success of it.The biggest brand in the mPOS market, a US company called Square, is losing money.  In Australia specialist providers include Mint Wireless. The accounting software company MYOB entered the market this year, offering a Mint Wireless device as part of an integrated sales and accounting package.PayPal launched an mPOS terminal, PayPal Here, in 2012 and upgraded it this year.Commonwealth Bank has two mPOS terminals - a high end device called Leo and an "on the go" terminal called Emmy, which was launched this year.Bendigo and Adelaide Bank entered the market last month, with a system called microPay.Westpac has announced that it have a similar offering some time this year.