Which of the following is not a type of oil usually referred to under Maine regulations?

No. 4 oil is not typically categorized under Maine regulations, as the state primarily recognizes No. 1, No. 2, and No. 6 oils. No. 1 oil is usually used for residential heating and has a lower viscosity, while No. 2 oil is a common fuel for heating systems with a higher viscosity suited for different applications, including commercial. No. 6 oil, also known as bunker fuel, is a heavy fuel oil primarily used in ships and large industrial applications.

The absence of No. 4 oil in the context of Maine oil regulations highlights the classifications that are actively monitored and regulated within the state, indicating that while it may exist in industry, it is not a standard classification for oil under Maine law. Understanding these classifications is crucial for compliance and for anyone involved in the oil industry in Maine.