Peel tomatoes (blanch if you hate peeling).  Use a food mill (or your hands) to remove seeds and separate juice.  Removing seeds improves flavor & texture.  Removing some juice will shorten cooking time.

Put tomatoes (will be mostly flesh) into a heavy saucepan (it’s OK if a few seeds sneak in).  Add onions, garlic, oregano, basil, salt, and oil.  Bring to a simmer. Cook until desired thickness.

Add 2 Tbsp lemon juice (or vinegar) to each quart jar (1 tbsp for pints).  Fill hot jars with spaghetti sauce.  Leave 1/2 inch head space. Wipe rims.  Adjust lids.  Process 45 minutes in boiling, hot-water bath* (35 minutes for pints).

Disclaimer:  Always follow directions specific to your equipment and elevation for canning.  Dispose of any home-canned goods that show signs of spoilage which can include: bulging lids, leaking, corrosion, cloudy, mushy, moldy foods or disagreeable odors.

*Hot Water Bath (45 minutes for quarts) is the processing method used for “Seasoned Tomato Sauce” in the Ball Blue Book.  It is what I have always used here in Kentucky for my spaghetti sauce.  Other sources and certain elevations require pressure canning for spaghetti sauce.  Please check the requirements for your area before canning.