If oil is in -- and it definitely is -- where's flavored oil?

So in that it's in-fused.

So in that supermarkets may soon be in-undated with enough flavors to have an Infused Oil of the Month Club.

So in that they are not in-expensive -- unless you make your own, which will make you appear to be in-genious.

But first, a bit about the trend.

Sales of olive oil in the United States have shown double-digit growth in the last 10 years. In much the same way that bottled water led to flavored waters, oil marketers have decided that there is money in oils that have gained flavor and aroma by having herbs and the like steeped or soaked in them -- hence the moniker "infused."

Infused oils are considered one of the fastest-growing segments of the oil market. At this year's Fancy Food Show in San Francisco, approximately 30 new infused oils were being hawked by companies to store representatives.

"This began about two years ago after restaurateurs began infusing oils as a way to add flavor without adding a lot of butterfat or other animal fats," said Ron Tanner, communications director for the National Association of the Specialty Food Trade.

A group of Napa County entrepreneurs is convinced there is a lucrative future in infused oils.

Napa Valley Kitchens, a merger of three companies, presented 10 flavored oils at the Fancy Food show. Four, produced by Michael Chiarello, chef and co-owner of Tra Vigne in St. Helena, have been sold nationally for some time under the Consorzio label.

Flavors you may have already noticed or sampled under that label are basil, roasted garlic, rosemary and porcini mushroom.

The flavors being added to those, either under the Consorzio label, the Napa Valley Kitchens or Napa Valley Mustard labels -- the two others in the new company -- are five-pepper, oregano, mustard, garlic, cilantro and jalapeno.

Ann Grace, director of public relations for the group, said a key to the quality of the oils is an infusion process that helps prevent oxidation and deterioration of flavors. The process was developed by Mr. Chiarello and Moshe Shifrine, a food technologist, former professor at the University of California, Davis, and a principal in Napa Valley Kitchens.

But, like many trendy "new" ideas in foodstuffs, infused oils were not just invented yesterday. Olive oil flavored with rosemary sprigs, chilies and herbs has long been common in Mediterranean cooking. There, it is often used in marinades or is served in a little bowl with fresh or grilled vegetables. The plain vegetables take on a whole new taste when the infused oil is drizzled over them.

The Chinese have been using chili-infused oils for centuries. Mustard-seed oil used in Asian and Indian cooking imparts a characteristic flavor.

Today's chefs are using flavored oils like condiments, to introduce flavor without pieces of herbal matter in the food or adding animal fats. When drizzled on a plate, lightly hued infused oils are decorative and flavorful.

Oils are 100 percent fat. But they have a high ratio of mono- and polyunsaturated fats to saturated fatty acids and so are considered healthier.

Even keeping in mind that oil is all fat, infused oils are nonetheless a bright and relatively healthful alternative to butter to drizzle over a baked potato. They can be used in salad dressings, marinades, in making mayonnaise, and to brush over pizza just out of the oven. They also give cooks a way to season without having to chop or buy ingredients that may be out of season.

These new oils sell for between $8 and $12, depending where you buy them, for a 12.6-ounce bottle.

You don't really need recipes to make flavored oil, but here are a few to get you started.

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Use this one on fish before grilling, brush on bread after grilling, pizza crusts after baking, or use to saute vegetables, meats, fish or poultry.

Roasted Garlic Oil

1 cup bland olive, canola or peanut oil

5 cloves garlic, peeled

Place the oil and the garlic in a saucepan over medium heat.

Cook until the garlic turns golden brown. Turn off the heat and cool the mixture to room temperature before pouring into a clean bottle with an airtight lid. Keep in a cool, dark place or refrigerate. It will remain flavorful for about 1 month.

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This oil, identical in flavor to the expensive brand on the market, is great for sauteeing mushrooms to intensify the woodsy flavor. Try cooking up portobellos to which you've added minced garlic and rosemary. Place the mushrooms on a platter, drizzle with balsamic vinegar and serve with crusty French bread.

Porcini Mushroom Oil

about 12 dried porcini mushrooms

about 1/2 cup hot water

2 cups pure olive oil

Rehydrate the mushrooms in the hot water until they are soft, about 10 minutes. Take the mushrooms out and pat them dry with a paper towel. Put the mushrooms with the oil in a microwavable dish and warm the oil slightly for 1 to 2 minutes, or until the oil feels warm to the touch. Set aside, uncovered, until the oil is cool. When completely cooled, cover and allow to steep in a cool, dark spot for a day or two. The oil will be fragrant and woodsy tasting in 24 hours, but the flavor will increase if you let it steep for another day or two before using. Strain out the mushrooms, if you like, before using.

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Use this in Asian salad dressings, to stir fry or make fried rice.

Spicy Pacific Rim Oil

Makes about 2 1/2 cups

1/4 cup sesame oil

1 1/2 cups canola oil

6 garlic cloves, peeled and crush with the broad side of a knife

1 tablespoon peppercorns

2 stalks lemongrass, outer leaves removed and chopped into 2-inch lengths

3/4 cup dried chili pods

1 2-inch piece fresh ginger root with peel, chopped

Combine all of the ingredients in a saucepan. Partially cover and cook over medium heat until the garlic turns a golden color. Turn off heat, cover and allow to cool. Take out the garlic and pour the remainder of the mixture into a sterilized glass bottle. Tightly cap the bottle and refrigerate or allow the mixture to steep in a dark, cool place for at least a month.

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This recipe, adapted from "The Glass Pantry" by Georgeanne Brennan (Chronicle Books, $29.95), gets a boost from lemon leaves from your own trees but I made it without them. It is very good on salads, potatoes and vegetables. Make sure to wash your lemons thoroughly, especially if you have purchased them. Citrus fruits are often heavily sprayed with pesticides.

Spicy Lemon Oil

Makes 1 quart

2 pounds (4 or 5) lemons

2 tablespoons coriander seeds

1 tablespoon black peppercorns

6 fresh lemon leaves (optional)

3 fresh or dried bay leaves

4 cups good-quality fruity olive oil

Cut each lemon into quarters. Put 1/3 of the cut lemons into a dry, sterilized jar with a lid. Sprinkle with about 1/3 of the coriander seeds and peppercorns, 2 lemon leaves, and 1 bay leaf. Make 2 more layers this way. Cover with the lid and allow to stand for 24 hours in a cool place.

The next day, pour the olive oil into the jar and cover it again. Let stand for 3 days. At end of 3 days, remove and discard the lemons. Strain oil through a sieve lined with several layers of cheesecloth. Decant into a dry, sterilized bottle. Seal with a cork and refrigerate. Will remain flavorful up to 1 month.

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This recipe is from Jim Tarantino's "Marinades" (Crossing Press, $14.95). It's good on cheese, vegetables and to prepare fish for the grill.

Oil Herbes de Provence

Makes 2 cups

1/2 cup extra-virgin olive oil

aflead,3 1 1/2 cups grapeseed oil, available at better supermarkets

3 to 4 garlic cloves

2 shallots, quartered

1 teaspoon fresh cracked black peppercorns

1 tablespoon dried parsley

2 tablespoons herbes de Provence (a blend of basil, fennel seed, lavender, marjoram, rosemary, sage, summer savory and thyme)

Combine the oils in a small, nonreactive pan. With a garlic press and strainer, press the garlic and shallots to extract juices. Discard the solids. Add the garlic-shallot juice, peppercorns and herbs to the oils. Simmer over low heat for 10 minutes. Cool to room temperature. Strain the oil, pour into a glass jar and refrigerate. This keeps up to o 3 months.

To chill or not to chill

Experts don't agree on whether you need to refrigerate oil infused with herbs or other foodstuffs.

If you listened to the federal and state governments, you'd refrigerate everything you plan to eat, but some food scientists disagree.

According to the Food and Drug Administation, all oils infused with garlic and onion should be refrigerated to prevent the possibility of botulism.

However, George York, extension food microbiologist emeritus at the University of California, Davis, food science and technology department, says microorganisms -- including those that cause botulism -- don't grow in oil. He says that if you are using dried herbs "you have no problem" not refrigerating an infused oil. If you use fresh herbs, the only bacteria that might grow would be harmless lactic acid bacteria. Even garlic bulbs won't cause a problem, he says. Mr. York says that if you're still worried, drop the garlic bulb in vinegar or lemon juice overnight before putting it in oil. Likewise, you can rehydrate dried ingredients in water spiked with vinegar.

You cannot preserve food in oil, he says, but oil that has, for example, a few mushrooms, garlic, peppers or whatever added to it doesn't require frigeration.

That said, other food safety experts insist chopped garlic in oil must be refrigerated to prevent dangerous organisms from growing. And, recently, producers of minced or crushed garlic in jars were forced to add citric acid to their product as a preservative.