I am running but I keep gaining weight?

I'm going to comment on the other user's answer that you burn 100 calories/mile.

That is simply not true. You burn calories based on the rate at which you run, how much you weigh, and the resistance (whether on a machine or running on a road).

The only solution is that you are eating more than you are burning. And some peoples caloric needs are different than others.

Sometimes your body can get used to cardio and therefore requires it in order to keep weight off, so if you stop doing cardio you may encounter a sudden weight gain.

It might sound wierd but you might not be eating enough... Your body might be keeping the fat instead of burning it off to use as energy. This happens when you're not getting enough nutrients from your food. Everybody's body is different in using energy so you should experiment with different diets. Maybe try a couple weeks without carbs and use a high protein diet, see what happens if it doesnt help or it becomes worse then try foods with a high healthy fat content like avacado, nuts, add in a few carbs and see how your body reacts.

Good luck!

I disagree with the above. I have lost 6 lbs during a 50 mile run before. And I am about 150lbs. Cardio is essential to good health. Counting calories does not always work like they say, it is a over simplified answer to a more complex system. If it is not Normal like you say and it continues you may want to get checked by a doctor to make sure there is not a serious problem.

Make sure you are eating enough so that your metabolism doesn't slow down. Try eating little meals 6x a day with a protein the size of your palm and a carb the size of your fist and dont forget veggies!! Fit in healthy fats they help you lose fat!!! Also you could have a mini meal as a protein bar or shake once a day each:) You should also have a day to eat whatever you want!! Believe it or not, it actually helps reset your metabolism and therefore to help you lose more fat!