Carlos Sainz Jr., the 17-year-old son of former world rally champion Carlos Sainz, is driving for Lotus GP in Monday's GP3 pre-season test session at the Circuit de Catalunya near Barcelona, Spain.

"In the last minute I had the chance to test in GP3 here," Sainz Jr. posted on Twitter late on Sunday.

Sainz is standing in for one day only for 18-year-old Finnish driver Aaro Vainio, who had to miss Monday's test day as he's taking an academic exam. Vainio had previously topped the timesheets on day two of the GP3 teams' first official preseason testing session at Estoril three weeks ago.

The Red Bull-backed Sainz Jr. had competed in Formula Renault 2.0 in 2011 and claimed the series title after an impressive 10 wins and eight pole positions during his season with Koiranen Brothers Motorsport. Sainz Jr. has also appeared in races in the Formula 3 Euro Series and had a full season in Formula BMW Europe in 2010.

Elsewhere on pit lane, new GP3 Series entrants Ocean Racing Technology were fielding their freshly announced 2012 driver-up of Carmen Jorda and Robert Cregan.

Jorda, from Spain, becomes the second female driver in GP3 after Trident Racing signed Italian race driver Vicky Piria for the 2012 season. Jorda has several seasons' worth of experience in European F3 Open, and in 2010 competed in four races of the Firestone Indy Lights Series for Andersen Racing. She previously took part in GP3 Series testing in 2009.

"I am eager to test the car that I am sure is very different from the Indy Light that I was used to," she said. "I'll be a rookie in the championship but I'm sure I'll improve race by race."

Irish driver Cregan spent 2011 in the V8 Supercar Series, competing in 17 races for Matt Stone Racing in the Ford BF Falcon. The 23-year-old also has previous experience in the UAE GT Championship and in Porsche Supercup, and had already tested with Tech 1 Racing earlier this year.

"The first race will be hard and I have a lot to learn," said Cregan. "I trust my own ability to adapt to this new reality and hope to gradually improve. I think I will be able to run in the top five in the short term."

His new team, Ocean Racing Technology, is making its first on-track appearance in GP3 this week after last week announcing that they are entering this year's GP3 Series, having reached a deal to take over the grid slot previously held by Tech 1 Racing.

"We are very happy to welcome Ocean Racing Technology to GP3," said series CEO Bruno Michel. "It is a great opportunity for the Portuguese Ocean's Racing team. This new season is set to be another thrilling one."

Ocean are now the fifth team to have presences in both GP2 and GP3, along with Lotus GP, Arden International, Carlin and Trident Racing. Ocean has competed in the GP2 Series since 2009.

"Our goal has always been to put in place a GP3 team as well," said Ocean's co-owners Jos? Guedes and Tiago Monteiro. "We did not expect it to be so soon, but the opportunity to take over from Tech 1 arose and we decided to take it."

Other new faces to be found in the GP3 paddock this week are Jenzer Motorsport's newly announced 17-year-old Russian signing Patric Niederhauser, and Status GP duo Kotaro Sakurai and Tom Blomqvist.

Carlin's line-up includes Alex Brundle and Antonio Felix da Costa while Kevin Ceccon will be among the drivers testing for Trident, while Atech CRS GP has Belgian driver John Wartique making his GP3 d?but appearance. However, RSC Mucke Motorsport will not be present, meaning that 26 drivers in all will be in action on Monday and Tuesday.

The weather for this two-day test is sunny and somewhat warmer than the unusually chilly conditions experienced last week by the GP2 teams testing at the same venue.

The first race of the GP3 season is on May 12 in Barcelona.