He passed the infirmary when Chief O'Brien stepped into the location and was later present in Quark's when Elim Garak collapsed. (DS9: "The Wire")
He listened Quark when the Ferengi told about his glorious fight against Kozak and how he killed him. Later, he joined the bar for a drink. (DS9: "The House of Quark")
In 2371 he was part of the bridge crew aboard the Defiant when they discovered the planet Meridian. He worked on the aft bridge when the planet suddenly appeared. When the crew investigated the dimensional shifts of the planet and its inhabitants, he manned the helm aboard the Defiant. Later he was back in the aft section, sitting at the table and also manned a side station. (DS9: "Meridian")
He served aboard the Defiant during the war between the Dominion and Starfleet and was among the crewmembers who were successful in their mission to destroy a Dominion facility near the Argolis Cluster. (DS9: "Behind the Lines")
He left Quark's and was talking to another man. They stopped their talk when Kira and Odo had their first kiss on the Promenade. (DS9: "His Way")
This Starfleet officer was played by regular extra Sam Alejan, who received no credit for his appearances.
This Starfleet officer served in the sciences division on board Deep Space 9.
He went to the Replimat and was talking to a Bajoran woman while Major Kira and Odo were talking about Odo's ability to eat. He then walked away but came back later while Tiron was talking to Kira and Odo. He later passed Tiron at the bar in Quark's and was also in Quark's when Major Kira entered and Quark announced her as his one millionth customer. While Kira and Odo were talking about Quark in the security office, he passed the office and went to a turbolift on the Promenade. He laster visited along with a female civilian Quark's again, he entered on the entrance of the second level and passed Quark and Tiron on their way to the holosuites. He later left Quark's along with a female command officer. They passed Odo and Major Kira who witnessed an angry Tiron shouting at Quark. (DS9: "Meridian")
He was among the crewmembers aboard the Defiant who were secured in their quarters when a Changeling saboteur took over the control of the ship. (DS9: "The Adversary")
He was on duty in sickbay after Rom became unconscious and assisted Dr. Bashir in his treatment. (DS9: "Bar Association")
She passed a gangway on Deep Space 9 shortly before Arissa, who hid herself, tried to get access to the station's computer for a second time. (DS9: "A Simple Investigation")
This Starfleet officer was played by regular extra and stand-inCathy DeBuono in one of her very first appearances on the series. She received no credit for it.
Science officer 2
This female science division ensign was among the crewmember who were evacuated from the habitat ring following an explosion in Miles O'Brien's quarters. She passed Major Kira. (DS9: "The Darkness and the Light")
This Starfleet science officer was wounded during the Dominion attack on Deep Space 9 in 2373. An operations division officer helped him on board the Defiant when Captain Sisko ordered the evacuation of Deep Space 9. (DS9: "Call to Arms")
This Starfleet officer was played by regular background actor Wade Kelley, who received no credit for this appearance.
Science officer 5
This female science division officer worked on the bridge of the Defiant during the final attack against the Dominion in the Dominion War. She manned an aft station when her console exploded and she fell over another console. Later, she was working on an aft station of the bridge. (DS9: "What You Leave Behind")
This science officer was played by stunt actress Linda Madalone, who received no credit for this appearance.
He attended the official ceremony on the bridge in which AdmiralWilliam Ross gave Captain Sisko the command of the starship. He left the bridge shortly before Ross told Sisko that another point of interest was on the PADD he gave the captain, the name change from Sao Paulo to USS Defiant. (DS9: "The Dogs of War")
This Starfleet officer was played by background actor Stephen Blackehart, who received no credit for his appearance.
On his official site, Blackehart named this officer "Lieutenant Pa'ak". 
Vulcan science officer
This Vulcan science officer served in the science division on board Deep Space 9 in 2372.
During the strike of the employees of Quark's O'Brien saw her and told Julian Bashir that she'll not join Quark's during the strike. He was right, she passed the establishment. (DS9: "Bar Association")