Comcast formalized its $30.7 billion bid for Sky, throwing down the gauntlet to Rupert Murdoch’s 21st Century Fox and Walt Disney as they vie for Britain’s largest pay-TV broadcaster.

Comcast is offering 12.50 pounds per Sky share in an all-cash deal, the Philadelphia-based company said in a statement Wednesday, confirming a proposed offer it made on Feb. 27. The offer is at a 16 percent premium to Fox’s 10.75 pound-per-share bid for Sky.

Media billionaire Murdoch must now decide whether to increase Fox’s bid to stave off Comcast’s challenge, raising the prospect of a bidding war. Fox, which already has a 39 percent stake in Sky, plans to sell the broadcaster to Disney as part of their $52.4 billion merger announced in December. In a separate statement, Fox said it remains committed to its offer for Sky and is “currently considering its options,” with a further announcement in due course.

Sky’s shares rose 3 percent to 13.40 pounds at 11.03 a.m. in London. Since Comcast announced its proposed bid in February, Sky’s shares had been trading at more than 13 pounds, at a premium to the Comcast price, as investors expected a protracted battle for the U.K. broadcaster.

“This might elicit the bidding war,” said Alex DeGroote, a media analyst at Cenkos Securities. “We now have a formal proposition, instead of just a suggestion. Sky at these levels is a free bet on the upside.”

Comcast said it expects the Sky deal to generate annual run-rate synergies of around $500 million, through a combination of revenue benefits and recurring cost savings.

“We have long believed Sky is an outstanding company and a great fit with Comcast,” CEO Brian Roberts said in the statement. “We very much hope that the independent committee of Sky directors will recommend our superior cash offer.”

Comcast said acquiring Sky would boost its ability to invest in programming, innovation and would significantly expand its international footprint. About a quarter of Comcast’s sales would come from overseas after a successful acquisition of Sky, compared to 9 percent currently, the company said said.

Fox is still awaiting regulatory clearance in the U.K. for its Sky bid, with a final decision from Culture Secretary Matt Hancock expected by mid-June.