This is how to do what you are saying. Create a class that extends WorldGenLakes and implements IWorldGenerator. Then, register a copy of it specifying your oil block as the block type.
import java.util.Random;
import cpw.mods.fml.common.IWorldGenerator;
import net.minecraft.block.Block;
import net.minecraft.world.World;
import net.minecraft.world.chunk.IChunkProvider;
import net.minecraft.world.gen.feature.WorldGenLakes;
public class OilLakeWorldGenerator extends WorldGenLakes implements IWorldGenerator{
// Constructors.
public OilLakeWorldGenerator(Block fluidBlock) {
super(fluidBlock);
}
// Methods.
@Override
public void generate(Random random, int chunkX, int chunkZ, World world, IChunkProvider chunkGenerator, IChunkProvider chunkProvider) {
int x = (chunkX*16) + random.nextInt(16) + 8;
int y = random.nextInt(256);
int z = (chunkZ*16) + random.nextInt(16) + 8;
super.generate(world, random, x, y, z);
}
}
Change the y when you want it to spawn at only certain levels.
