Electrical Energy: read the Firm meter in kWh for a certain period, say weekly or monthly.

Petrol and gas: you can get the consumption from the finance department or inventory department.

Some unseen consumption must be recognized.

I hope I understood your question and gave a right answer,

continued:

You can also read the value in an hour interval, for the hole year.

Simple computer program may be written implemented to show the trends of consumption.

Before installing an industrial firm, a pilot plant "a smaller model" is constructed. One of the basic measurements & calculations that are done, at this stage, are the ones concerned with mass & energy balances. As for the energy, both the energy input "consumption" & the energy output are found out.

Upon moving up to the industrial plant, there are scaling-up calculations but these will give a close but not the final depiction. When the firm starts operating, more precise data are collected. These data may be written down on the combined-detailed flow sheet of the whole plant.

Do not expect to see this flow sheet since it is usually a "secret". Also, do not expect to get the "true" energy consumption bill of the firm from its owners or managers. You will be alright, if they give you figures that do not contradict with scientific thinking or reasoning.

It all depends on how big the company is. Sometimes individual departments of the company consume a lot of energy and this can disrupt knowledge.

contact energy auditors who have done study, if they have done something in that firm