What is a good substitute for oyster sauce (for someone with a shellfish allergy)?

The most widely-accepted substitute seems to be various sauces made from mushrooms. I don't want to say "mushroom sauce" because most products don't have that exact name. For example:

Here you have "Vegetarian Mushroom Flavored Stir-Fry Sauce" on the left, and "Premium Shitake Mushroom Flavored Soy Sauce" on the right. I'm actually not familiar with the one in the middle and not sure what the whole label says - it might be the same as the first.

If you go to a specialty Asian food store, you might actually find a product called "vegetarian oyster sauce", which is pretty much the same thing.

Failing that, you can always substitute soy sauce, or hoisin sauce if you want a less watery texture. They won't be exactly the same, but it's the same general idea (dark, fermented, salty sauce rich in glutamates).

"Fish sauce" will be very close to oyster sauce in taste, but may still contain shellfish, so be careful.

Try black bean sauce. The body and color of the sauce is similar, though there are coarse bits of bean in it (where oyster sauce is usually smooth).

Add a shake of fish sauce to taste.

Fish sauce alone may be too thin. Most fish sauces are fermented anchovies with added salt (and maybe sugar).

I just taste tested this (have all the ingredients) and it's a good substitute.

My grandmother makes vegetarian egg rolls for me. She uses a vegetarian oyster sauce you can find it at pretty much any Asian food store. It tastes the same as the original sauce.

My recipe from what I had in the pantry... frozen cooked black beans (3tbls)/4 teaspoons sugar/ a sachet of paste for Miso soup/ 1 teaspoon balsamic vinegar syrup / 1 teaspoon chinese 5 spice, ...It's as close as I'll get with what's on hand.

A mixture of Hoisin and fish sauce will be close to what you seek as Fish sauce is very thin and watery whereas Hoisin sauce is thick, but sweeter than oyster sauce.

I Heart Umami has a great vegetarian oyster sauce made with shiitake and dates. The sauce tastes really umami rich and I love that it has no additives and easy to make. https://iheartumami.com/vegetarian-oyster-sauce/

You can restore the thickness by combining the soy/mushroom sauce with a cornstarch slurry... Remember oyster sauce is also about adding body and thickness to the sauce... I would use a combination of light and dark soy, and perhaps a little sugar to bring back the sweetness.

There's a recipe I use for Chinese greens in garlic. It involves frying about a clove of chopped garlic per helping in a neutral oil, not too hot, until it is just off turning golden. Not as far as you would go for garlic oil. To that I add (again per helping) a tablespoon each of dark fermented soy and water, and a teaspoon of sugar, mixed to a thin slurry with no more than a half-teaspoon of cornstarch. Cooked just far enough to thicken, before tossing the steamed vegetables in it.

Although it lacks some of the fishy complexity, it is very close to oyster sauce.

There are several oyster sauce substitute options that are shell-fish free. Each comes with it’s own advantages and disadvantages.

Soy sauce is the main ingredient in oyster sauce and probably your best choice. The two sauces have similar tastes, to the extent that adding Worchestshire sauce usually gets rid of any distinguishable differences and it's shellfish free!

You could also try a fish sauce, but be careful when reading labels because some are shellfish free but not a lot aren't.

Another option is mushroom sauce, which has the added bonus of being vegetarian (if you or a friend are), and is super easy to make yourself.

I am allergic to mullosk and shellfish too but use thai fish sauce with no problem. I have eaten seskatchuan beef too and had no issue.(this is supposed to contain oyster sauce) if you are at the beginning of your allergy, you still can try this. Do not use Indonesian shrimp paste, it will trigger a reaction for sure. I have been allergic for over ten years now and get a reaction from even slight bits of mullosk or shellfish, but fish sauce is ok. Hope this helps.

Soy sauce was best for me plus other websites suggested it to.

Most store-bought sauces contain fillers/preservatives/etc. I avoid additives like the plague (migraines are my particular plague). I've made my own Asian style sauces and one of my secret ingredients is molasses. It allows for a good approximation of those tasty brown sauces in Chinese take-out and thickens the sauce. I too, use fish sauce as an alternative when trying to approximate oyster sauce. There are lots of home-made sauce recipes online.

Made a great Asian beef and broccoli dish tonight and it was really, really good! I substituted black bean sauce for the oyster sauce and my sauce was delicious. The recipe I followed called for reduced salt soy so I just mixed some dark (full salt) soy with the low salt soy to make up the amount the recipe called for. Maybe 1/4 dark soy to 3/4 reduced salt. The black bean sauce worked well as a substitute.