Place the tomatoes in a large pot over medium heat. Add salt, pepper, oregano and sugar. Cook for about 15 minutes, then using a potato masher, press them gently.
Reduce the heat to medium- low and add the garlic. Simmer for about 1 hour, then using the masher again, press until obtain the consistency desired.
Add the basil and olive oil and continue simmering for about 1 ½ hour more.