Both teams had a couple of good chances but Southend were denied by the woodwork and Oldham could not find a way past visiting goalkeeper Darryl Flahavan.
The result means injury-hit Southend are now three points clear at the top of League One, while Oldham move up to the edge of the play-off places and have gone five home matches without defeat.
They came close to an early goal through defender Guy Branston, but Southend hit the post on 15 minutes when skipper Kevin Maher was unlucky with a powerful drive from the edge of the box.
Oldham also hit the post with a free-kick from Richie Wellens which flew across goal from the left-wing and was grabbed by Flahavan on his line.
There were few chances in the first half but Flahavan needed to be at his best on 51 minutes when Andy Liddell unleashed a pile-driver from the edge of the box.
Maher was just off target from similar distance and Southend were left frustrated on 64 minutes when Efetobore Sodje, making his debut after signing from Yeovil, headed a free kick against the bar from close range.
Oldham dominated the last quarter of the game and Luke Beckett could have scored his fourth goal in successive matches but fired off target with just the keeper to beat.
David Eyres shot at Flahavan, who made a stunning save in the 89th minute when he flung himself away to the right and kept out a low volley from Oldham striker Paul Warne.
Southend's only chance in the closing stages fell to Wayne Gray, but he could not get the ball from under his feet and sent a shot straight at Chris Day in the Oldham goal.