The NFL players’ union and the NFL owners will continue, for the 13th day, to try and work out how to split the roughly $9 billion in annual revenues.

NFL Commissioner Roger Goodell and union executive director DeMaurice Smith and their negotiating teams were at a federal mediator’s office Tuesday for the labor negotiations.

New York Giants owner John Mara and Washington Redskins general manager Bruce Allen were among those accompanying Goodell.

The NFL Players Association group included union president Kevin Mawae and several current or former players, including Cardinals kicker Jay Feely, Colts center Jeff Saturday, Chiefs linebacker Mike Vrabel and Ravens cornerback Domonique Foxworth. Mawae flew in from Nashville on Tuesday morning; he was one of seven of the NFLPA’s 11 executive committee members attending Tuesday’s session at the Federal Mediation and Conciliation Service.

Top NFLPA outside counsel Jeffrey Kessler did not arrive at the mediator’s office when others did Tuesday morning. He also wasn’t present Monday, when talks resumed after a break over the weekend.

The current collective bargaining agreement originally was set to expire last week, but two extensions have now pushed the cutoff to the end of Friday.

What will happen the rest of this week is still anyone’s guess. If a deal isn’t reached, the sides could agree to yet another extension and negotiate beyond Friday. Or talks could break off, leading to, possibly, a lockout by owners or antitrust lawsuits by players.

The NFL has not lost games to a work stoppage in nearly a quarter-century. By agreeing to continue with mediation, the league and union made it clear neither was quite ready to make the drastic move of shutting down a sport that is more popular than ever. The past two Super Bowls rank No. 1 and No. 2 among most-watched TV programs in U.S. history.

The old CBA was agreed to in 2006, and owners exercised an opt-out clause in 2008, leading to the current stalemate.

Money, not surprisingly, is at the center of it all.

One person with knowledge of the negotiations told The Associated Press last week that the NFLPA has not agreed to any major economic concessions – and that the NFL has not agreed to the union’s long-held demand that the league completely open its books and share all financial information.

The person spoke on condition of anonymity because mediator George Cohen insists that everyone involved stay mum about the substance of the talks.

The key issues have been:

-How to split revenues, including what cut team owners should get up front to help cover costs such as stadium construction and improvement. Under the old deal, owners received about $1 billion off the top. They entered these negotiations seeking to add another $1 billion to it.

-A rookie wage scale, and where money saved by teams under that system would go.

-The owners’ push to expand the regular season from 16 games to 18 while reducing the preseason by two games.

-Benefits for retired players.

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