Global Motorsport Media
Kamui Kobayashi has admitted he had a difficult season as 'lead driver' with Sauber in 2011.
As a rookie, the Japanese spent his first full season in F1 in 2010 alongside highly experienced teammates Pedro de la Rosa and Nick Heidfeld.
But this year, the 25-year-old shared the Swiss team's garage with rookie Sergio Perez, ultimately finishing the season with double the Mexican's haul of points.
Kobayashi, however, admits that the role as the key Sauber driver "certainly wasn't easy for me".
"I needed to improve a lot in various areas. Not only in driving, but also in making decisions with the engineers."
It was important to have an emotionally positive finish to the season
Sauber team boss Peter Sauber has decided to keep both Kobayashi and Perez, 21, for 2012.
"It was important to have an emotionally positive finish to the season," Sauber wrote in Blick newspaper. "This was especially true for Kobayashi, who has a difficult year behind him."