This is a job for a professional pressure washer. High water volume, 5.5 gpm or better, with heat 200 degrees or better 1000 - 1200 psi for gum, won't harm the concrete.
Oil stains do soak down below the surface, but to get the surface oil off and lighten the stain, use EBC cleaner, or sodium Hydroxide diluted, pressure washer with heat and a surface cleaner at about 800 psi. I use the sodium first then let dry then apply EBC. When the concrete is dry the stain will be invisible, when it rains it is back but not on the surface.
Concrete is porous and translucent, so the stain down deep can be seen but it won't affect texture or get tracked. To hid what is left then paint the concrete, if it is small add some Portland cement, broom in and then wet down.