Adding oil to pasta water does not prevent sticking as well as many people think. Oil floats on top of the water instead of coating the pasta evenly while it cooks. Pasta usually sticks because surface starch becomes tacky during the first few minutes, so early stirring is far more effective. Oil can also create a slippery layer after draining, making it harder for sauce to cling. For better results, use plenty of boiling water, stir immediately, salt for flavour, and finish the pasta with sauce plus a little starchy pasta water.