The Ireland lock, who captained the Lions in 2009, has missed most of the season due to injury.
The 33-year-old's fitness problems had looked likely to rule him out of this summer's Lions tour to Australia, but Gatland has said that O'Connell's recent form has caught his attention.
"Definitely he was one that caught the eye. It will be interesting to see how he goes over the next couple of weeks," Gatland told MSN Sport.
"It was a very dominant performance from a very experienced player. You would expect him to come out and stamp his authority on the game - he did that and definitely took the eye of a number of people including ourselves particularly at line-out time, around the field and his leadership qualities.
"His successes have been with Munster and Ireland but probably if he looks back on his career he'd love to go on another Lions tour and get win a series in the Southern Hemisphere. It's something not a lot of players have achieved."
The first Test against Brisbane takes place on June 22.