At the Sahlen’s Six Hours of the Glen, it’s often a crapshoot whether to run two drivers or three.

The field is pretty much split in half this weekend for the IMSA WeatherTech SportsCar Championship between the two options.

In Prototype, 12 of 16 cars have a third driver. That number drops to just two of eight cars in GT Le Mans. Only BMW Team RLL runs three in that class (including Bill Auberlen, right). But in GT Daytona, it’s 10 of 18 cars.

All told that means there are 24 of 42 cars this weekend that opt to run a third driver.

Heat and drive time are key to note this weekend, when you consider running two or three drivers.

The upwards of 90-degree temperatures for Sunday means single stinting drivers may be the case, and doubles aren’t as prevalent.

At Watkins Glen in the Prototype and GT Le Mans classes, the base drive time is only 30 minutes.

GT Daytona meanwhile requires a one-hour, 30-minute base and minimum drive time. Once all three drivers run that time, you’re only left with one hour and 30 minutes still to fill.

The maximum drive time for all classes is four hours.

For some drivers, having a chance to race as a third driver means an opportunity to showcase themselves for a potential full-season drive in 2019. For others, it’s the last chance to moonlight in IMSA for the year if another racing assignment comes first.

One such driver who faces the latter dilemma is Olivier Pla, who shares the No. 2 Patron Nissan Onroak DPi with Ryan Dalziel and Scott Sharp. Pla races for the Ford GT team in the FIA World Endurance Championship. This means he’ll race in Fuji, Japan in October instead of Motul Petit Le Mans.

“Watkins Glen is one of my favorite tracks in the world. With all the high speed corners, this place is just amazing and driving a DPI car here you need a lot of commitment,” said the Frenchman. “It’s going to be my last race this year with the Patrón ESM boys because of the Fuji clash. I really want to finish with a strong result here!”

Other drivers like Gabby Chaves have an opportunity to shine in their role. The Colombian American IndyCar driver stands in at Action Express Racing for the injured Joao Barbosa this race as the third driver for the No. 5 Cadillac DPi.-V.R.

“The first thing is of course that you never want to have an opportunity because someone got hurt. So this is an unfortunate circumstance with Joao (Barbosa) having his injury,” Chaves said. “But I appreciate the opportunity to join the championship-leading team.

“I’m excited to be going back to endurance racing. With different classes all racing at the same time, there is a lot for the driver to deal with as you work through traffic.”

Here’s the third drivers for this weekend’s race for full-season IMSA entries.

Note: Cars 32 (United Ligier) in Prototype and Cars 51 (Spirit of Race Ferrari), 64 (Scuderia Corsa), 69 (HART Acura), 71 (P1 Mercedes), 75 (Riley/SunEnergy1 Mercedes) and 96 (Turner BMW) either are part-time entries or have rotating driver lineups, so aren’t listed in the above table.