Britain's Piggy French lies in second place with the previous day's leader, Lemington Lett Dance (42.7) and is third with her Greenwhich test run winner, DHI Topper W (43.1).
• William Fox-Pitt is in first and third positions after the dressage in the eight and nine-year-old British Championships.
Oslo leads with 42.3 penalties, overtaking first-day leader, New Zealand's Mark Todd with NZB Campino (43.1). Fox-Pitt's Lionheart is in third with 47.9.
"Oslo did a lovely test," Fox-Pitt said. "He was a bit spritely but both these horses were in need of a run and will be aimed for Pau."