If I eat one pound of pure fat will I gain more than one pound of body weight?

Close. There are 3500 calories per pound of body fat. In order to lose just one pound of stored fat we need to burn off 3500 extra calories OR retain 3500 extra calories to gain one pound. A pound of butter has around 3200 Calories.

https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Miscellaneous/2007_September_7

Hi zbeck.

A gram of fat has 9 calories per gram, 453.6 grams per pound = 4082 calories per pound of fat.

http://www.nutristrategy.com/nutrition/calories.htm
http://answers.google.com/answers/threadview?id=555411

So theoretically - if I could stomach a pound of fat, I would gain more than a pound.

Eat Butter...it's less fattening than Olive Oil.

Ounce for ounce, olive oil is one of the most fattening, calorically dense foods on the plant; it packs even more calories per pound than butter (butter: 3,200 calories; olive oil: 4,200). Based on data from USDA Nutrient Database for Standard Reference, Release 13. U.S. Department of Agriculture, Agricultural Research Service, 1999:

Serving Size 1 stick (113.400000g)
Calories 813 Calories from Fat 809

http://annecollins.com/calories/calories-butter-margarine.htm
http://www.nutrientrich.com/blog/?p=216

So.... If I ate a pound of Olive Oil, would I gain more than one pound.

4200(Olive Oil) - 3500(human pound) = 700(calories)

Speaking ONLY to the fat consumed, yes...you should gain 1.2 pounds.