I'm a EE in the Oil/Natural Gas industry in the US. We design electrical systems for midstream plants. So basically we're the guys who get the oil from drilling stations, then process it to separate all the different gasses and oils mixed in the liquid before shipping it to upstream plants for distribution.
For the oil industry:
Very very basic math at the Algebra level. Believe it or not we don't use calculus at all. As we like to put it "If you're solving equations you're doing something wrong." In Oil 90% of what we do is based off tables from the NEC (Natoinal Electric Code). You have tables for motor HP vs FLA, Cable/Conduit sizing vs Current, etc. At most, you need basic understanding of power calculations for 3 phase AC motors. The most math I've ever had to do is solve KVA = AVsqrt(3)/1000 to figure out the total KVA load on a bus in order to size it properly.
In the midstream oil industry you basically get a list from a process engineer of all the different motors, pumps, fans, heaters, heat trace cables, panels, etc. that will go into the plant. We then take this data and make schematics for a Motor Control Center building which will provide power as well as control systems to all the equipment. Controls are basic out-of-the-box PLC controllers we buy that are programmed by a technician in the field. We figure out needed circuit breaker sizes for each motor (based off tables), needed wire sizes to properly withstand the current used to power the motors (tables), needed sizes for the main cable busses (KVA equation), needed length/power output of heat trace cable to ensure pipes don't freeze in winter time (via a Heat Trace software tool), needed transformer sizes to step down voltage from 4160 to 480 to 240 to 208 (via tables).
An entry level engineer for the oil industry just needs an EE degree with basic understanding of simple power equations (think on the level of P=I*V). The rest is learned through experience and by working on projects. When we get new engineers who start here they're given a copy of the NEC as reference and taught how to properly size all equipment for best efficiency and cost.
When I graduated college I knew almost nothing about sizing motors or the NEC. Like I said most of it is learned from experience and "just doing it" which is something our employers understand when hiring an engineer. The truth of a BS EE degree is in college you learn how to learn, then when you start a new career in any field your employer will take the time to teach you advanced concepts specific to that industry.