(REUTERS) -- McDonald's Corp (MCD.N) reported quarterly profit that beat analysts' estimates as sales, which were already outpacing competitors, picked up strength in December.

The company and its franchisees have been pouring money into their restaurants at a time when smaller and financially strapped chains are slashing costs.

Such investments in renovations, longer operating hours and new menu items have helped McDonald's win market share from weaker rivals.

Sales at stores open at least a year rose 9.6 percent in December, with a 9.8 percent increase in the United States and a 10.8 percent increase in Europe.

Analysts on average forecast a 5.9 percent increase overall, with the a 5.4 percent increase in the United States and a 6.4 percent increase in Europe, according to Thomson Reuters I/B/E/S.

The world's biggest hamburger chain reported fourth-quarter profit of $1.38 billion, or $1.33 per share, up from $1.24 billion, or $1.16 a share, a year earlier and beating the average analyst estimate of $1.30 a share, according to Thomson Reuters I/B/E/S.

Revenue rose 10 percent to $6.82 billion, edging above the average analyst estimate of $6.81 billion.

McDonald's shares were up 40 cents at $101.35 in premarket trading on Tuesday.