To follow the abbreviation for USA posted yesterday, I thought I should post state abbreviations today.

Use the U.S. Postal Service format (two letters, no periods) when you must abbreviate state names. In running text, unless the copy is a lengthy list of place names, it’s preferable to spell out the state name, especially if your audience might include international readers. Note that the third example needs semicolons between entries because individual items in the list include commas.

• The class of 12 included students from Alaska, Colorado, Connecticut, Georgia, Montana, Minnesota, and West Virginia.
• Research was conducted in Mesa, Arizona, and Las Vegas, Nevada.
• Those responding to the call for special funds included alumni from Harrisburg, PA; Fargo, ND; Miami, FL; San Jose, CA; Midland, TX; Shreveport, LA; and Hope, AR.

From the University of Colorado at Boulder Style Guide