Mixing graduate students with undergrads usually works as well as blending oil with water. But put them together in an overcrowded Palo Alto bar hosting simultaneous events, add in long lines and missing wristbands, and voila: the mixture is a recipe for disaster.

Senior Night and Graduate Pub Night were held at overlapping venues in Palo Alto late Thursday night, leading many students who attended to complain about overcrowding and long lines.

Organizers of Senior Night — better known as “Pub Night,” the semi-regular senior outing to local bars — said they were not informed until too late that graduate students would also be at Nola’s, one of the places they had booked for themselves. But since organizers do not reserve Senior Night venues for exclusive use, they had no choice but to share the space with hundreds of graduate students.

Graduate Pub Night organizers admitted some lapses in planning, but promised the oversights would be ironed out in the future as the event is held more regularly.

“That was an oversight on our part,” said Annemarie Baltay, one of the graduate organizers. “We should have double-checked to make sure that undergrads wouldn’t be there.”

Seniors were caught by surprise by the number of graduate students at Nola’s.

Utsav Sethi ‘07, like many other seniors, left Nola’s and Old Pro — the official Senior Night venues — for other bars in Palo Alto soon after arriving.

“I was pretty disappointed, and it was crowded,” he said. “Pretty much everyone felt that way. There were a lot of non-seniors there. A lot of people were looking forward to it, since it was the second-to-last Senior Night and all.”

Meanwhile, graduate students, enjoying their first Pub Night since autumn quarter, showed up en masse, causing their own logistical problems. Organizers estimated that over 200 graduate students — up from 50 in the fall — attended the event at Nola’s, spurred in part by graduate student-only drink discounts that event organizers arranged with the bar beforehand.

“It was way more people than I expected,” Baltay said.

The large turnout also outstripped the drink-discount wristbands. As a result, many students demanded discounts from the bar despite lacking a wristband to prove their eligibility. Bartenders, unable to determine who was a graduate student and who was not, refused to grant the special prices to anyone without a wristband.

“We can’t give out discounted drinks to just anybody,” said John Mylod, a manager at Nola’s. “When it comes to the wristbands, you have to be able to take care of that stuff. You can’t expect us to do it for you.”

As the year winds down, organizers for both events say that a similar conflict is unlikely to occur in the future. And if they never meet up again, it will suit both parties just fine.

“Ideally, we wouldn’t want to go to the same place,” Baltay said. “Let the senior class have their fun and let grad students have their fun.”

The next Graduate Pub Night is scheduled for May 31 at Nola’s.