Series or finish in one?

When you're writing the book and the story just keeps going and going, so you finish the story or do you make it into a series? Series can be a continuation of the same storyline with the same characters, they can be a continuation of characters that in the first book were in the background, or it can be just a continuation of the same type of story but entirely different story. What will it be? For me a couple of my books have stood alone completely. I knew and felt good with ending them at the words The End. But some of my stories needed more. Some were supposed to be stand alone but the characters just pulled at me to be more. In my latest book, Open The Heart, I originally planned on it being alone. As I delved into the story around 3/4 of the way in I knew it had more to tell. You may be saying why not just go ahead and make it a mega novel with 50,000 or more words, but in some instances it's good to just end on a cliff hanger, leaving the reader wanting more. In Victoria I knew at the start that it would be a Saga. I knew as I was writing the first chapter how it would end and I built it up to that major cliff hanger which of course has garnered lots of readers writing to me stating that they were hanging on pins and needles. I just smile and know I did the right thing. It's had several asking when the next book could be expected. What's funny is they always ask what happens? I can't tell you until the next book comes out is always my response. So, what will you next book be? It's sometimes a hard question. Does your story line have the stamina to carry on for several books? Does your general premise for the book have series quality? Well, let me know how you figure it out. As always, good writing and May God Bless You...