Neat! Could you explain your process a little? Looks like a tablet was used.
Sure. It's a little hard to explain but I'll give it a shot. I basically start with a black background and work my yellow over the top in layers so if I screw something up along the way it's easy enough to go in and fix it or undo it.
What I started with is the lasso tool. I drew a lasso shape similar to a peanut and used that basic shape for the majority of the design. I then smooth the lasso shape by about 30-40 pixels. Since I'm using a mouse to draw them, this gives the shapes a nice smooth curvature similar to a french curve. Next, I invert my selection and using a soft brush I paint around the edge of my shape moving from inside the center of the shape gradually moving out further along the edge and then as I come around the other side of the 'peanut' I work back in towards the center. I set my brush opacity at anywhere between 3% and 10% and work slowly and gradually build my highlights for a more organic natural effect. This process produces a curved flame with soft fading tips. Next, I continue to do the same thing, sometimes moving the same 'peanut' around the screen, and sometimes creating a new peanut to work from. In the crotch of each flame I like to have at least three layers to give more depth and dimension to the flames.
Once I'm done painting my flame, I can copy, paste, skew, resize, mirror, etc. until I have it exactly like I want it then position it where I want it. Once it's positioned, I can go over that layer with a soft eraser and remove certain parts of each new flame layer to make it all blend better. Once everything is how I want it, I flatten and bump the contrast just enough to bring the brightest areas to about 100%
I hope that all makes sense.