Finding my gerbil a mate

Ive had a gerbil for about 9month he lives by himself in a gerbilarium. I want introduce him to a friend i was just wondering what the best way to introduce another gerbil as i know they can be aggresive and which sex is best?
   
Thanks

Hi,
   
Please see these links below:
   
http://www.petpeoplesplace.com/resources/advice/small/100-will-single-gerbil-get-lonely.htm
   
http://www.petpeoplesplace.com/resources/advice/small/165-should-my-grieving-gerbil-get-companion.htm

Same sex pairs is best.
   
The most common way to introduce two gerbils is to use the split cage method.
   
First you need a 20 gallon (long is best) aquarium. Then you need to place a wire divider in the middle of the cage. Place a gerbil on either side. About everyday or so switch the gerbils around to get them use to one another's scent. After about a week of doing this have another cage ready that neither gerbil has been in before. Put both of the gerbils in the cage. Watch them carefully and brake up any fights. Once you feel they are okay together you can put them in their permanent home and watch them for the next few days to make sure no fights brake out.