Updated: Nov 17, 2020
There can be multiple inventors on a patent. But who owns the patent can be difficult to answer in the absence of an agreement.
Frequently, multiple people get together to design a new product. Often, they do so with an unspoken understanding that they will all share equally in the venture. But as also happens often, there is no written agreement that addresses the rights and responsibilities of each "partner."
Disagreements arise, and everyone is unclear as to who or what entity owns the invention or patent. And everyone is unclear if he/she can break away from the group and continue the project on their own.
In the absence of an agreement, each inventor would jointly own the patent. That means that each inventor is free to exploit the patent without the other inventors. Therefore, each inventor can make and sell the patented invention. And if the inventor does so successfully, the inventor does not have to share the profits with the others.
However, an agreement among the inventors could be written or oral. If it is oral, things can get complicated. The inventor who splits off from the group may have one understanding of what was the agreement about patent ownership and splitting of profits. The others who remain may have a different understanding.
What can complicate things further is when an entity (e.g., corporation) has been formed by the inventors. Then the question is whether the entity owns the patent or the inventors do so. In the latter instance, the inventors may have just licensed the patent to the entity.
The lesson here is that a written agreement about patent ownership can help avoid a lot of disputes including litigation.