Spring question: Who fills out the rotation?

Note: This is part of a series analyzing the questions facing the Texas Rangers as spring training gets set to begin.

Today's question: Who fills out the starting rotation?

The Rangers are in the process of adding an external option to the rotation race, agreeing to terms on a minor-league deal with Tommy Hanson, pending a physical, according to sources. One source said it's likely that Hanson would make one salary at the big-league level and another at the minor league level, depending on whether he makes the club. You can read more about Hanson here.

But the club also has some internal options already set to compete for the rotation, which currently consists of Yu Darvish, Matt Harrison, Martin Perez and Alexi Ogando. Not only does the club need to find that final starter, but also see what kind of depth options exist if another injury pops up (and it inevitably will). Let's take a brief look at some of the internal possibilities for the rotation:

Nick Tepesch: The right-handed hurler has worked on a changeup this offseason that he hopes to incorporate more into his repertoire, which includes a sinker and slider. He was 4-6 with a 4.84 ERA in 17 starts and two relief appearances. But if Tepesch, who doesn't throw particularly hard, can add the changeup and mix his pitches, he believes he can show quick and marked improvement.

Michael Kirkman: He went from spring training star to struggling starter in a span of a month. It was an odd 2013. The 27-year-old was dominant in spring training and looked poised for a solid season in the bullpen. But he was 0-2 with an 8.18 ERA in 22 innings and a 2.318 WHIP. No reliever with at least eight innings pitched had a worse WHIP.

Kirkman looked at video and worked with his coaches and quickly discovered it was all mental. He is confident he's in a better place, thanks to hard work and some tweaks in his mechanics that he him feeling more comfortable.

Robbie Ross: He went to winter ball knowing that he needed some more work to be in the best position to compete for a starting job, something he really wants to do. The lefty struggled against left-handed batters last year, something he'll have to improve upon to be a viable starter. He's now had a couple of spring trainings and knows what to expect, not to mention some important experience over the past two seasons in the bullpen. It will be interesting to see how much winter ball helped him and how he does this spring.

Tanner Scheppers: The youngster is realistic about his desires for the 2014 season: He wants to start or close. Those are his goals. But he comes into spring training stretched out to start and that's his focus. Scheppers did well as a setup man last year and could end up in that role again. He was 6-2 with a 1.88 ERA and a 1.07 WHIP, bouncing back in September after a rough August. Scheppers has started before in his career, making seven starts at Triple-A in 2010. But he's been a primarily a reliever since then.

Colby Lewis: Remember him? The veteran is hoping to make a comeback and the Rangers are excited by what they've seen on video of Lewis throwing at his home. He'll be on a different schedule from the other pitchers as he comes back from hip surgery, but we'll see how far he can come in one spring training. Lewis, of course, has vastly more experience than the other candidates and was the club's top postseason pitcher in 2010 and 2011 as the team went to two consecutive World Series. Lewis hoped to return last year and it just didn't happen. But he's ready to put two years of injuries behind him. He's a wild card in that it's unclear how soon he'll be ready.

Others will likely emerge and we'll see if the Rangers bring any additional arms to camp in addition to Hanson. But that final rotation spot should be one of the biggest storylines of the spring.