I seem to be hit or miss with my bread. It tastes great but I never get a good oven spring and/or too dense. How do I get my loaf from somewhat flat to nice and round and airy inside.

Here's the recipe I've been using from off a google search:

Ingredients
* 1/2 cup (4oz/115g) sourdough starter (fed / active)
* 1 cup (8floz/225ml) lukewarm water
* 2 tablespoons olive oil
* 2 3/4 cups (14oz/389g) bread flour*
* 2 teaspoons salt

I Add ingredients and bulk ferment for 18 hrs. The. I let it proof after forming a ball for 2 hrs. Bake at 450 covered for 30 min. Then remove cover for another 20-25 minutes.

Try a pinch of baking soda right after the ferment. Like 1/8 teaspoon.

Based on your 18 hour bulk ferment and 2 hours of proofing, my guess is you are overproofing your loaves. Try going by feel rather than time. Watch some videos about proofing bread and checking using the finger dent test.

Are you getting good volume growth during ferment and proof?

Thanks.

Yes I am getting great volume on ferment but very little rise on the proofing.

You could be too warm of an environment. 18 hours is a long time for as warm as our houses tend to be.

Buy Tartine book. Follow directions. Weigh ingredients. Take water temps. Be strict.

You'll have really really good bread.