One under-the-radar method for teams to add organizational depth each offseason is through minor-league free agency. There are three different types of minor-league free agents: (1) players who have completed their initial seven-year minor-league contract without re-signing or being added to the 40-man roster; (2) players who are outrighted to the minors but elect minor-league free agency in lieu of accepting the outright assignment (to be eligible, players must have at least three years of major-league service time or been previously outrighted); and (3) minor leaguers who have been released. Additionally, major-league free agents unable to land a major-league deal can sign a minor-league deal.

If a player on a minor-league deal later proves worthy of being added to the big club, his contract is purchased by the major-league club and is added to the 40-man roster. The calendar for minor-league free agency generally is early November to early March.

More often than not, minor-league free agents end up filling out the holes in a club's Triple-A roster, ultimately to be used as major-league emergency depth. However, it's not uncommon for minor-league free agents to be assigned to Double-A and Class A affiliates. Every so often, and in a trend that is becoming increasingly popular, teams will sign minor-league free agents to major-league deals. For example, Baltimore signed left-hander Kelvin De La Cruz to a major-league deal in November, despite him having no major-league experience.

The Red Sox typically sign about 15-20 minor-league free agents each offseason, with varying degrees of success. In fact, Boston has signed 85 minor-league free agents over the last five offseasons (not including this offseason). Of those 85 players, 22 have gone on to play with the major-league club, 37 spent the rest of their time in the minor-league system and 26 were released before even playing a game (major league or minor league) for the organization.

Successful minor-league free-agent signings over the past few seasons have included:

• Third baseman Brandon Snyder, who, despite what the final number may show, filled in adequately for 27 games in 2013 while Will Middlebrooks was optioned to Pawtucket. Snyder recently re-signed a minor league deal for 2014.

• Shortstop Pedro Ciriaco, who hit .281 in 104 games for Boston in 2012-13 before being traded to San Diego in June 2013.

• Right-hander Aaron Cook, who started 18 games for Boston in 2012, posting a 5.65 ERA -- a passable showing given that he was in the majors on a prorated $1.5 million salary.

• Righty starter Justin Germano, who posted a 2.40 ERA in 16 starts for Pawtucket in 2012 and pitched 5 2/3 scoreless innings for Boston before being traded to the Cubs for cash considerations.

• Journeyman reliever Vicente Padilla, who appeared in 56 games for the Red Sox in 2012, posting a 4.50 ERA. Like Cook, Padilla played with Boston for a $1.5 million prorated salary.

• First baseman Mauro Gomez, who played in 37 games for Boston in 2012, hitting .275/.324/422. He was waived in a roster crunch prior to start of the 2013 season.

• Lefty reliever Andrew Miller, who technically was acquired in a trade for lefty Dustin Richardson in November 2010, non-tendered and released three weeks later, and then signed to a minor-league deal two weeks after that. He has pitched in 107 games over three seasons with the Red Sox, posting a 4.24 ERA, and is expected to be a valuable contributor to Boston's 2014 bullpen.

• Rich Hill, a veteran left-hander and Greater Boston native who signed a minor-league deal with the Red Sox in June 2010, then went on to sign two additional minor-league deals with the club in December 2010 and December 2011. He posted a 1.14 ERA in 40 games for the Red Sox, spending a large portion of his time in the system on the disabled list.

• Versatile outfielder Darnell McDonald, who played three seasons with the Red Sox, posting a .735 OPS in 234 games. He was released in June 2012 and has gone on to play in the Yankees' and Cubs' systems.

• Infielder Angel Sanchez, who played very well with Pawtucket in 2010 and appeared in one game for Boston. In July 2010, he was traded to Houston for backstop Kevin Cash when the Red Sox were in dire need of catching depth after placing both Victor Martinez and Jason Varitek on the disabled list. Sanchez went on to start for the Astros for the remainder of the season.

• Utilityman Nick Green appeared in 104 games with Boston in 2009, playing six positions. He has since played with the Dodgers, Blue Jays and Marlins.

At this point in the 2013-14 offseason, the Red Sox have signed only five minor-league free agents: left-hander Tommy Layne, right-handers John Ely and Dayan Diaz, utilityman Mike McCoy and third baseman Carlos Rivero. The club ultimately may bring in fewer minor-league free agents this offseason than in prior years due to the expanded depth of prospects at the Triple-A level.

Layne, 29, made 40 appearances out of the San Diego bullpen between 2012 and 2013, primarily as a left-handed specialist. In all, he compiled a 2.85 ERA and 1.07 WHIP, striking out 31 and walking 8 in 24 1/3 innings. He struggled with control in 2013, walking 27 in 46 Triple-A innings and five in 8 2/3 innings at the big league level. He's expected to work out of the Pawtucket bullpen this season, but certainly could be used out of the Boston bullpen at some point.

Once a well-regarded prospect, Ely was traded to the Los Angeles Dodgers as part of a deal for outfielder Juan Pierre in December 2009. He made his major-league debut the following season and pitched in 25 games for the Dodgers between 2010 and 2012, going 5-13 with a 5.70 ERA. Traded to the Astros following the 2012 season, Ely injured his elbow in his 2013 debut at Triple-A Oklahoma City. The injury necessitated Tommy John surgery, and he missed the rest of the season. Given the usual recovery time for the procedure, Ely is questionable for the start of the season. When he returns, he is likely to provide depth for the PawSox rotation.

Diaz, still only 24, is still somewhat of a prospect. A smallish lefty out of Columbia, he has a live arm, capable of throwing his fastball in the mid-90s. He has had an injury-riddled career, but showed flashes of brilliance with the Astros' organization in 2011 and 2012, striking out 134 in 108 1/3 innings between Short Season-A Tri-City and Low-A Lexington, compiling a 1.91 ERA. Having only pitched in five games at Double-A, Diaz likely would be slated to pitch with Double-A Portland in 2014. If he returns to his 2011-12 form, he may get look at Pawtucket or even Boston in late 2014.

A 12-year veteran of professional baseball, McCoy saw major-league playing time with Colorado in 2009 and Toronto from 2009 to 2012. In 140 games across those four seasons, he hit .190/.273/.256 while playing every position except for catcher. Boston fans may remember him for pitching the ninth inning of a blowout loss for Toronto against the Red Sox in June 2011. McCoy spent all of 2013 at Toronto's Triple-A affiliate in Buffalo, hitting .245/.357/.327. He'll be a utilityman with the PawSox in 2014 and provide emergency depth for the Red Sox.

A 25-year-old third baseman, Rivero spent all of 2012 at Triple-A Syracuse, hitting .303/.347/.435 in 126 games. He got a long look in 2013 spring training with the Nationals, appearing in 30 games, and was one of the team's final cuts. Out of options, Washington was able to clear Rivero through waivers and outright him to Triple A. He split the 2013 season between Syracuse and Double-A Harrisburg, hitting .242/.298/.328. He's seemingly on the bubble for a roster spot between Portland and Pawtucket this spring, and where he ultimately lands may be more of a function of where the club decides to start Garin Cecchini.