Oxygen loves hydrogen. Hydrocarbons have lots of hydrogen. Oil is hydrocarbon.

Add enough energy to start the chemical reaction, and BOOM. Along with all the things that go with exothermic and expansion reactions (ie, your foot gets blown off, and anything that can burn in the area likely will be)

Also, get things hot enough with oxygen around, and things you think can’t burn, will. Including steel.

Look up oxygen compressor fires. It’s scarily interesting.