Though the string quartet failed to make the top three in last weekend's final, Cowell is convinced that the girls can match the success of his operatic pop group Il Divo.
"Escala are the most marketable act to come out of Britain's Got Talent by a country mile," a source told the News of the World. "By signing with Simon at the Sony BMG record label they're getting all the expertise that helped Il Divo shift a whopping 30 million records and become the world's favourite opera hunks.
"A British and US No1 album is already pencilled in as a near certainty. Their great strength - apart from their natural beauty - is the ability to appeal across markets. They'll be an inspiration to the younger generation of music lovers, but will also reach out to classical fans."
The group, which consists of violinists Izzy Johnston and Victoria Lyon, viola player Chantal Leverton and cellist Natasya Hodges, are believed to have signed their contracts on Friday. Later, they performed at the first night of the Britain's Got Talent tour in London.
They had previously been tipped for success after impressing Cowell at the semi-final stage of the ITV1 talent series.