Only the largest fields are likely to appear on sectional charts, but many smaller fields are noted on terminal area charts. In some cases, such as Delta Farms south of New Orleans, they so prominent that they are used as VFR reporting points for nearby airports.
Oil and gas fields are identified by a collection of small circles outlined in black. These circles approximate the relative position of each rig or tank. While these rigs may take any of a variety of shapes and forms, it's worth noting that some are quite tall and may be surrounded by support cables that could endanger an aircraft that is flying too low.