The NFL and the NFL Referees Association made enough progress in negotiations Tuesday night that the possibility of the locked-out officials returning in time to work this week's games has been discussed, according to sources on both sides.

An agreement in principle is at hand, according to one source familiar to talks, although NFL owners have postured with a "no more compromise" stance.

The possibility of NFLRA referees working Thursday's Ravens-Browns game is dim, according to sources, but it is possible they could work games on Sunday and Monday.

The officials, if the agreement in principle is finished by Thursday, could meet in Dallas on Friday and take any tests to enable them to work games Sunday and Monday.

Talks continued past 11 p.m. ET Wednesday night between the two sides.

One source says the difference between the NFL and the referees "is about $2," while another source described the talks as "the league wants double sausage and the referees want soy-free cheese."

Although league sources said it would take a week to get the locked-out officials on the field, the NFLRA says its 121 referees have been trained on the new rules implemented last season, have already passed physicals or are prepared to pass physicals immediately. New official game uniforms designed by Nike are "hardly an obstacle," according to a source.

Both sides have made concessions on previous sticking points such as a taxi squad of 21 new officials and pension plans that sources say the final meaningful hurdle is, as one source said, "about a little more money."

While league sources say owners who participated in a conference call with commissioner Roger Goodell during Tuesday's talks had instructed the negotiating team to set a firm barrier for the financial settlement, the NFLRA is prepared to accept a new agreement primarily in the form of a "ratification bonus," which would compensate its 121-member union for concessions it is willing to make.

The NFLRA and the league have all but agreed on developing a 21-member "taxi squad" that Goodell has pushed, but not at the financial cost of the union members.

The NFLRA, citing that it once utilized the now-defunct NFL Europe as a training ground of prospective officials, is willing to train 21 officials from the major college ranks by including them in offseason seminars as well as incorporate them in training camp work.

The NFLRA would not unionize those officials and would want them compensated by the league if "they are brought up from the minors" to work a regular-season game.

Goodell has wanted the power to "bench" officials who underperform or are downgraded during the season. The NFLRA contends the league already has that ability because there are always between one and four crews that sit home each week and would be more qualified to substitute in such a scenario.

The NFLRA also wants to form an "expert committee" that would be major contributors to the league's stated goal to improve officiating. Under this proposal, the committee would be comprised of some of the top retired officials and supervisors of major college conferences who had served as NFL officials.