Advice on this topic varies.
As noted in a commnet webpage with a section about “Numbered, Vertical ("Display"), and Bulleted Lists”, with emphasis added,
Writing and reference manuals offer different advice for creating lists. It seems that as long as you're consistent within your document, you can devise just about any means you want for creating your lists, whether you want them as run-in lists (built into the flow of your text) or as vertical lists (indented and stacked up). Technical writing may have its own requirements in this regard, and you should consult a technical writing manual for specific rules. Use parentheses around the numbers (no periods after the number, though) when using a run-in list:
I have three items to discuss: (1) the first item; (2) the second item; and (3) the third item.
Use semicolons to separate the items, whether they're expressed as fragments or full sentences.
An ehow webpage offers a slightly different form (in its step 2):
Write a run-in list. List items in a simple sentence, using commas to separate items. Write, for example, “Wendy added vanilla, flour and sugar to her famous cookie recipe.” Or itemize more complex ideas with numbers and semicolons to separate sentence fragments. Write, “We propose three points of consideration: 1) park fees; 2) daily traffic; and 3) environmental impact.”
A prismnet webpage says:
With in-sentence lists, there are no conventions when to use letters (a), (b), and so on, as opposed to numbers (1), (2), and so on. If you are in a numbered list and need a sublist, use letters, to contrast with the numbers. Otherwise, there really seem to be no widely agreed-upon guidelines—just be consistent!
A grammar.quickanddirtytips webpage suggests avoiding run-in lists when there are many items:
Letters are also often used when you have a list in which the items don’t need to be in a particular order, but you want to keep them in a sentence instead of listing them vertically. The letters can call extra attention to each list item, but if you’re putting in letters to separate list items in a sentence, you should also ask yourself if it might be easier for your readers to digest the material if you listed the items vertically.
Roman numerals, particularly lowercase (i), (ii), ..., are alternatives to letters and numbers. For letters and Roman numerals I prefer the two-parenthesis (·) syntax to the single-parenthesis ·) syntax, using the latter only for numbers. The prismnet webpage shows lowercase letters, (a), (b), ..., which are an acceptable alternative to (A), (B), ... . Some sources recommend using letters when the order of items is relatively unimportant, and using numbers otherwise;
but for sets of related documents I suggest using the same convention for run-in lists in all cases, rather than sometimes using numbers, sometimes letters, and sometimes Roman numerals.
