Is the following sentence missing one or more commas? If it is, where?: The lions waited in the tall grass as the gazelles grazed completely oblivious to their presence.

This is a complex sentence.

By AP style, it needs not any COMMA.

because it is a COMPLEX SENTENCE.

The lions waited in the tall grass---this part is an independent clause. "as" part is a dependent clause.

Needs not any COMMA.

One moment, the old version of the British grammars like Oxford and Cambridge use a COMMA somewhere before starting the dependent clause I usually see even to the famous Mag. in The Economist.

So, I usually advised my IELTS test takers ( not TOEFL/GMAT) follow the Oxford /Cambridge dictionary to ensure their good score for trickery motion.

But AP style and Webster dictionary don't use it I often see. Now, you people take your decision.

The sentence is missing one comma, which joins the dependent clause ("completely oblivious to their presence") to the independent clause ("The lions waited in the tall grass as the gazelles grazed"). There is no comma after "grass" because "as" means "while," not "because," in the sentence.

The dependent clause also needs clarification as "their" refers to the lions, not the gazelles ("completely oblivious to the lions' presence").

Yes, the sentence is missing a comma. It should be placed after "grazed": "The lions waited in the tall grass as the gazelles grazed, completely oblivious to their presence."