* TSX up 121.74 points, or 0.94 percent, at 13,088.23
* All 10 of the main groups are higher
By Solarina Ho
TORONTO, June 28 (Reuters) - Toronto's main stock index marched higher on Tuesday morning as optimism over a resolution to Greece's sovereign debt woes buoyed investor appetite and helped drive commodity prices higher.
The overall energy group led advances and was up 1.45 percent. Suncor Energy SU.TO was the most influential gainer on the index, nearly double the percentage rise of the next biggest mover. Suncor rose 2.33 percent to C$37.82.
Cenovus Energy CVE.TO was not far behind, rising 3.14 percent to C$34.45.
Crude prices extended gains as risk appetite improved on hopes that a resolution would be reached soon on Greece's debt problems. [O/R]
Royal Bank of Canada RY.TO was the second most influential gainer, climbing 1.08 percent to C$54.48. The overall financial group, which makes up about a third of the index, was ahead 0.62 percent.
The materials group, home to mining firms, climbed 1.04 percent, led by a 1.20 percent rise by Barrick Gold ABX.TO. The gold miner was trading at C$43.10.
At 10:57 a.m. (1457 GMT), the Toronto Stock Exchange's S&P/TSX composite index .GSPTSE was up 121.74 points, or 0.94 percent, at 13,088.23. All 10 of the index's main groups were higher.
"Markets are very thin, very volatile. We're waiting on the Greek situation," said Irwin Michael, portfolio manager at ABC Funds, noting that Thursday was both the month- and quarter-end, with Friday a holiday in Canada and Monday a U.S. holiday.
"Some people are just walking away, letting the market finish wherever it will ... people want to just balance out their portfolios for the year's quarter-end. It doesn't take very much to move the market up either way."
Michael also pointed out that the weakness in the market over the last two months probably means it's a little oversold and that it was due for a recovery.
"There's been a fair amount of negativity factored into the marketplace, so it doesn't take very much to move it back up," he said.
In corporate news, Westport Innovations WPT.TO, which announced it was developing a natural gas engine technology with General Motors, saw its shares jump more than 10 percent to C$23.57. [ID:nL3E7HS27R]
On the downside, Yellow Media YLO.TO was one of the index's biggest decliners, extending Monday's dramatic losses and falling another 11.30 percent to C$2.12, amid worries over the telephone directory publisher's struggle to transition from print to digital. [ID:nL3E7HR2BG]
($1=$0.98 Canadian) (Reporting by Solarina Ho)