US online job ads fell by 138,500 in September to approximately 5.28 million, according to The Conference Board’s report on online job ads released today. September’s decrease follows a gain of 34,200 in August and leaves the third quarter of 2015 with a small over-the-quarter decline of 21,000 job ads.

“Labor demand in 2015 started with a very strong first quarter, followed by losses in the second quarter and an essentially flat third quarter, leaving the average monthly increases in 2015 at a modest 18,000 per month,” said Gad Levanon, managing director, macroeconomic and labor market research for The Conference Board. “While the number of ads flattened in recent months, it remains at a very high level, suggesting a strong labor demand.”

In September, three of the largest online job categories posted increases while seven posted decreases.

Computer and mathematical science ads posted the largest gain, up 11,100 to 601,200. Healthcare practitioners and technical ads rose 7,100 to 623,000 and management ads gained 3,900 to 495,700.

Office and administrative support ads posted the largest decrease, down 20,300 to 560,200. Food and preparation- and serving-related ads fell 13,000 to 228,000, while transportation ads declined 11,700 to 401,700.