Jupiter has the strongest gravitational pull because of it’s large size. The more mass an object possesses, the more gravitational pull it creates. Jupiter is the most massive planet. Europa's gravity is only about thirteen percent that of the earth. It's distance from Jupiter varies, and the moon's near side feels Jupiter's gravity more strongly than it’s far side.
The magnitude of this changes as Europa orbits, and this creates tides that stretch and relax the moon’s surface. As Europa moves away from Jupiter, Jupiter's gravitational force decreases, which causes Europa to return into a more spherical shape and producing tides in its ocean.