Average fixed mortgage rates in the U.S. fell in the latest week, with the 30-year rate remaining near May 2013 lows, according to mortgage-finance company Freddie Mac (FMCC).

"Mortgage rates fell for the third consecutive week as oil prices plummeted and long-term treasury yields continued to drop despite a strong employment report," Freddie Mac Chief Economist Frank Nothaft stated Thursday.

For the week ended Thursday, the 30-year fixed-rate mortgage reached 3.66% on average, the lowest level since late May 2013, when it was 3.59%. The 30-year rate was 3.73% the previous week and 4.41% a week earlier.

Rates on 15-year fixed-rate mortgages averaged 2.98%, marking the first time they have fallen below 3% since May 2013. A week earlier, the 15-year rate averaged 3.05%, compared with 3.45% a year earlier.

Five-year Treasury-indexed hybrid adjustable-rate mortgages, or ARMs, on average, was at 2.9%, compared with 2.98% the previous week and 3.1% a year earlier. One-year Treasury-indexed ARM rates on average were 2.37%, from 2.39% the previous week and 2.56% a year earlier.

Write to Tess Stynes at tess.stynes@wsj.com

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