I have read many topics on this and I cannot get any of the solutions to work.

#include <SDL/SDL.h>
#include <SDL/SDL_image.h>
#include <SDL/SDL_opengl.h>

int main(int argc, char *argv[])
{
    SDL_Surface *screen;
    if ( SDL_Init(SDL_INIT_VIDEO) != 0 ) {
        printf("Unable to initialize SDL: %s\n", SDL_GetError());
        return 1;
    }

    SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );

    screen = SDL_SetVideoMode( 128, 128, 32, SDL_OPENGL );
    if ( !screen ) {
		printf("Unable to set video mode: %s\n", SDL_GetError());
		return 1;
	}

	glClearColor( 0, 0, 0, 0 );

	glEnable( GL_TEXTURE_2D );

    glViewport( 0, 0, 128, 128 );

    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();

    glOrtho( 0, 128, 128, 0, -1, 1 );

    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();

    GLuint texture;
    SDL_Surface *surface;

    if((surface=IMG_Load("gradient.png"))) {
        glGenTextures( 1, &texture );
        glBindTexture( GL_TEXTURE_2D, texture );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
        glTexImage2D( GL_TEXTURE_2D, 0, 3, surface->w, surface->h, 0,
                      GL_RGBA, GL_UNSIGNED_BYTE, surface->pixels );
        SDL_FreeSurface( surface );
    }
    else {
        printf("SDL could not load gradient.png: %s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }

	glClear( GL_COLOR_BUFFER_BIT );
    glBindTexture( GL_TEXTURE_2D, texture );

    glBegin( GL_QUADS );
        glTexCoord2i( 0, 0 );
        glVertex3f( 0, 0, 0 );

        glTexCoord2i( 1, 0 );
        glVertex3f( 128, 0, 0 );

        glTexCoord2i( 1, 1 );
        glVertex3f( 128, 128, 0 );

        glTexCoord2i( 0, 1 );
        glVertex3f( 0, 128, 0 );
    glEnd();

    SDL_GL_SwapBuffers();

    SDL_Delay(7000);

    glDeleteTextures( 1, &texture );

    SDL_Quit();

	return 0;
}

This came from a tutorial by Kyle Foley. I just condensed the code so there would be less scrolling. I also modified it to load from a PNG file, for the OpenGL texture to use RGBA, and the like.

I have attached gradient.png to this topic. I am baffled at what to do to get alpha blending working. Thank you!

Your call to glTexImage discards the alpha channel since you only request a texture with three color channels. The third parameter is equivalent to GL_RGB, which means the texture contains a red, a green and a blue channel, but no alpha channel. Use GL_RGBA instead.

This is one of the things I tried a while back on my own. I should have included that change in the source code I posted. The result remains the same even when changing 3 to GL_RGBA as you mentioned. I just now tried it again. It couldn't be my computer or anything, could it? Have you tested this? Thank you for your response!

Applying both of your solutions to the file works... looks like I was trying them individually before when trying to solve the problem on my own. A reputation++; for the both of you! Thank you!