I just got one its: Obligatory
The American Heritage Dictionary has over 3 1/2 pages of words that begin with "ob". You would get a much more comprehensive answer by looking for it, rather than asking for it.
Words that begin with the prefix "ie" include "ielectric," "iefficient," and "iempower."
opposed That starts with "op" not "ob"
The prefix for "oblivious" is "ob-." In this case, "ob-" is a prefix that means "against" or "towards." When added to the word "oblivious," it changes the meaning to suggest a lack of awareness or consciousness towards something.
The prefix of "obtrusive" is "ob-".
The prefix of "oblige" is "ob-".
The prefix of "obsess" is "ob-".
Some words that begin with the prefix "ambu" include ambulance, ambulatory, and ambulate.
incredible
insert
outside
Some words that begin with the prefix "aug" include: augment, august, augur, and augury.
Words that begin with the prefix "ir" and mean "not" include irregular, irresponsible, irrelevant, and irrational.