Comcast and Disney (Fox) Battle Again. This Time for British Broadcaster Sky.

Control of a $30 billion company doesn’t often come down to an auction. But that is the fate of British broadcaster Sky, one of Europe’s most valuable television businesses.

To determine control, a showdown between Comcast and 21st Century Fox (through the auspices of its soon-to-be owner, the Walt Disney Co.) is scheduled to start Friday evening. Over the next day, Comcast and Fox will duel it out for Sky. The winner of the auction will be announced Saturday evening London time, pending no major changes to the process.

Rupert Murdoch had long sought to acquire the 61 percent of Sky that Fox (and, earlier, News Corp.) did not own. His most recent takeover effort began in late 2016.

Then in December, 21st Century Fox struck a $52.4 billion deal to sell the bulk of its assets to Disney, including its 39 percent stake in Sky.

But Sky was a key target in what became a complex bidding war between Comcast and Disney. Comcast made a higher takeover offer this spring in part to spoil Disney’s bid to acquire most of Fox. The situation effectively leaves Fox trying to acquire Sky on behalf of Disney, and it and Comcast both increased their offers.

Then in June, Comcast made an offer worth $65 billion for Fox’s businesses. The spoiler bid forced Disney to increase its offer by $19 billion, adding to Disney’s debt.

Disney prevailed but did not gain control of Sky, which Robert A. Iger, the head of Disney, had called “a real crown jewel.”

Fox has offered 14 pounds per share (valuing the company at $32.5 billion). Comcast has countered with 14.75 pounds per share ($34 billion). But neither offer was considered best and final, prompting Britain’s Takeover Panel to force both parties into an auction.

Sky shares have been trading above 15 pounds — well above roughly 10 pounds at the start of the year — in anticipation of even higher bids.

The auction rules, published Thursday, describe three rounds of blind bidding. But several factors could complicate the process beyond simply sorting out who offered the higher price.

— Comcast wins with a bid of 14.75 pounds

Round 1: Fox-Disney goes first since it currently has the lower offer. It could keep its bid at 14 pounds, which would be a calculated move to force Comcast into bidding against itself.

Round 2: Comcast’s turn. The bids are blind, so Comcast won’t know if Fox-Disney has raised its offer or not. If Comcast senses it would be bidding against itself, it might leave its offer at 14.75 pounds.

No Round 3. Comcast wins.

— One side wins with a higher bid by Round 2

Round 1: Fox-Disney raises its bid above 14 pounds.

Round 2: Comcast raises its bid, and the two offers are not equal.

No Round 3. The higher offer wins.

— One side wins with a higher Round 3 bid

Round 1: Fox-Disney raises its bid.

Round 2:Comcast’s bid matches Fox-Disney’s Round 1 offer.

Round 3: Both parties put in their best and final offer, and the higher offer wins.

— Fox-Disney wins with a bid equal to Comcast’s

Round 1: Fox-Disney bids.

Round 2: Comcast’s bid matches Fox-Disney’s Round 1 offer.

Round 3: Here is where a twist could add a complication. Either side can make its final-round offer contingent on both parties making a bid.

In other words, if Comcast makes its Round 3 offer contingent on Fox-Disney bidding and Fox-Disney doesn’t bid, Comcast’s offer is null. In that case, there’s no Round 3 and we’re back to Round 2 with the equal bids.

In that case, the matter would be handed over to Sky’s independent directors, who would evaluate each offer based on the likelihood of completing the deal. That means determining how many more shares either party has to buy to gain control. Fox-Disney has a head start here since it already owns 39 percent. Based on its most recent stated offer, the company plans to amass 75 percent of the company, which means it needs to buy only 36 percent for control.

But Fox-Disney could lower that threshold to 51 percent at any time, meaning it would have to buy only 12 percent of outstanding shares. That would be appealing to Sky’s board. In this narrow outcome, Disney could effectively get control of Sky relatively cheaply.

For Comcast, it has to own 50 percent plus one share for control, giving it a higher threshold to meet.

In that case, Fox-Disney wins.