Power in negotiations comes from:
1. Constructive Power
This is your ability to satisfy the other party's interests (needs). What are they really after? You need to ask questions, watch body language and do your research.
2. Obstructive Power
You have power that comes from you ability to block the satisfaction of the other side's satisfying their interests (needs).
3. Jumping Power
This is your ability to leave a negotiation and is typically linked with how good your alternatives (BATNA) are.
4. Personal Power
This is your desire, confidence, skills, and knowledge (DECKS) to succeed. Some describe these components as the intangibles or art of negotiation.
Some other sources of power:
1. The power to satisfy another's interests (underlying needs)
2. The power of knowlege, expertise, and/or a particularly elegant, moral, or ethical solution
3. The power to give another credit or special recognition
4. The power to apologize
5. The power of your alternatives: your alternative(s) if you do NOT do the deal
6. The power of alliances