Do I have to use oil when making pie crust?
Oil is not substituted for eggs, as it has completely different properties. It is normally substituted for the solid fat. 

While it is certainly possible to do it this way, it is much fussier than just using solid fat. It requires frequent trips to the refrigerator during making if you want to end up with a solid crust and not just a pap. You have to be well experienced with pie doughs to be able to recognize exactly when to put it into the refrigerator or freezer. The result is not all that different for solid fact, except for 1) taste, if you use some strongly flavored oil (like one of the toasted nut oils), and 2) bragging rights that you pulled it off. 

If you are just looking for an easy recipe, use one with solid fat (butter, lard or shortening; shortening is easiest to work with but has the least taste) and adhere to the instructions. You will recognize a good pie crust recipe by following criteria: 


it warns you against overmixing the butter and flour 
it tells you when to refrigerate 
it also mentions what kind of texture it produces (although in some cultures where only one type of crust is desired, e.g. flaky for American pies, this may be missing). 
it uses reasonable ratios. This would be between 3:2 and 2:1 for flour to fat by weight, maybe a little outside this range. If it contains any other ingredients beside egg, water and sweetener, they should be in very small amounts (tablespoons or even teaspoons). 
if it is sweet, it does not use normal sugar. It uses either confectioner's, or some liquid sweetener. 
generally, a recipe given by weight is more trustworthy than one by volume. I have made many recipes by volume which did work, but because they are riskier, pros prefer to work by weight. With volume, you never know how well developed the recipe is before you start, and never know if you will achieve the same ratio or if mismeasurements will ruin a recipe which worked perfectly well for the author.