The Department of Energy yesterday charged five major oil companies with overcharging various customers by more than $100 million.

As part of a continuing audit of all the major companies by the DOE special counsel's office, yesterday's filings represent only a small portion of several enforcement actions expected to be filed before the end of the year.

The department has assessed overcharges against the following firms: Arco ($67.9 million), Exxon ( $24 million), Conoco ($2.2 million) and Amoco ($770,507). The four were given notices of probable violation. None was charged with any wrongdoing.

In three other related cases, firms consented to overcharge accusations, and agreed to refund violations. Exxon agreed to pay $5.6 million, Union Oil paid $2.4 million and Conoco consented to pay $914,000.

All of the allegations involve violation of complex pricing and allocation regulations put into effect in 1973.

Amoco was specifically charged with overpricing condensate liquid, which is subject to crude oil pricing regulations.

Conoco was accused of reporting excessive natural gas liquid costs.

Exxon allegedly overcharging customs through miscalculating the volume of internally consumed products.

Arco was accused of improperly computing transportion costs which are passed through to final purchasers. It was also accused of changing its accounting method for determining crude oil costs.

DOE has already charged the oil industry with some $5 billion in overcharges for various violations of regulations. Further accusations of at least another $5 billion in over charges are expected to be aired before the end of the year.