McGee's on Food and Cooking states that once opened
Pasteurized milk stored below 40°F/5°C should remain drinkable for 10 to 18 days.
It continues on the different types of pasteurization (bold mine)
There are three basic methods for pasteurizing milk. The simplest is batch pasteurization, in which [...] a few hundred gallons [of milk is heated at] 145°F/62°C for 30 to 35 minutes.
Industrial-scale operations use the high temperature, short-time (HTST) method, in which milk is pumped continuously through a heat exchanger and held at a minimum of 162°F/72°C for 15 seconds. [...]
The third method of pasteurizing milk is the ultra-high temperature (UHT) method, which involves heating milk at 265-300°F/130-150°C either instantaneously or for 1 to 3 seconds, and produces milk that, if packaged under strictly sterile conditions, can be stored for months without refrigeration. [...]
Sterilized milk has been heated at 230-250°F/110-121°C for 8 to 30 minutes; it [...] keeps indefinitely at room temperature.
I would assume that longer pasteurization (e.g. 3 seconds) and the higher temperatures (e.g. 150°C rather than 130°C) could add a few months before the milk starts to spoil.