(Reuters) - U.S. cable company Comcast Corp's CMCSA.O proposal to buy Sky Plc SKYB.L for $31 billion has raised the specter of a potential bidding war between with Rupert Murdoch's Twenty First Century Fox FOXA.O and Walt Disney Co DIS.N.

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Comcast, the owner of NBC, MSNBC and Universal Pictures, said on Tuesday it proposed to offer 12.50 pounds per share for Britain’s Sky, more than the 10.75 pounds that Fox has agreed to pay for it.

Murdoch’s Fox agreed to buy the 61 percent stake of Sky it did not already own in a cash deal in December 2016, but the takeover has been held up by regulators over concerns the media tycoon wields too much influence in Britain.

In December, Disney agreed to buy a number of Fox assets, including Fox’s stake in Sky, in a separate $52-billion deal.

The next likely step is Comcast makes a firm offer, which would require the company to have its funding in place. Fox then could return with a higher offer.

Here are some of the scenarios on what may lie in store next for Sky:

FOX RAISES ITS BID

The most likely scenario, according to many analysts, is that Fox, with Disney’s blessing, raises its bid, potentially prompting a bidding war with Comcast. Fox has to at least match Comcast’s bid, but analysts estimate a final winning bid for Sky could go as high as 14 to 15 pounds per share. Sky’s shares jumped Tuesday 20 percent, closing at 13.31 pounds, above Comcast’s offer.

Under the terms of Fox’s deal with Disney, Disney cannot bid for Sky on it own, so any bid would come from Fox. However, Disney CEO Bob Iger has spoken about the importance of Sky to Disney’s plan to launch a global online streaming service. So it is likely that Disney would back Fox in bidding higher.

COMCAST WINS MAJORITY STAKE IN SKY

Fox could choose not to challenge Comcast, which has said its offer is contingent on acquiring more than 50 percent of Sky. Comcast would prefer to own the whole of Sky, so Fox could use its 39 percent stake in the company as a bargaining chip.

Once the its deal with Fox closes, Disney will own a majority stake in online streaming service Hulu in which Comcast is also a shareholder. Some investors have speculated that Disney could swap its controlling stake in Hulu as part of a deal for Comcast’s stake in Sky.

Comcast is currently bound as a passive investor of Hulu, meaning it cannot buy more shares in the company, under its consent decree with the U.S. Department of Justice when it bought NBCUniversal. However, that consent decree expires in September.

GOING ALL IN

There is an outside chance that Comcast could engage with Fox about buying the assets Disney is buying. Comcast had bid $60 billion before losing out to Disney, and sources have told Reuters that Comcast has been discussing bidding for the Fox assets again.

But such a deal would face significant regulatory hurdles in the U.S., which previously prompted Fox to snub Comcast’s bid. There is no reason to believe that Fox’s assessment of the regulatory risk will change.