In most lists, a writer will use a comma to separate the listed items. Some lists, however, include items that already contain commas, in which case adding more commas to the punctuation mix just becomes confusing.
In such cases you can use semicolons rather than commas to separate the items. That way your reader will easily be able to identify the boundaries between each item. Make sure to include the semicolon even before the “and.” For example:
He had written about the gas, electricity, and paper markets; the healthcare industry; and an assortment of regulatory and enforcement agencies.