The current recommendation is to use python -m pip, where python is the version of Python you would like to use. This is the recommendation because it works across all versions of Python, and in all forms of virtualenv. For example:

# The system default python:

$ python -m pip install fish

# A virtualenv's python:

$ .env/bin/python -m pip install fish

# A specific version of python:

$ python-3.6 -m pip install fish

Previous answer, left for posterity:

Since version 0.8, Pip supports pip-{version}. You can use it the same as easy_install-{version}:

$ pip-2.5 install myfoopackage

$ pip-2.6 install otherpackage

$ pip-2.7 install mybarpackage

EDIT: pip changed its schema to use pipVERSION instead of pip-VERSION in version 1.5. You should use the following if you have pip >= 1.5:

$ pip2.6 install otherpackage

$ pip2.7 install mybarpackage

Check https://github.com/pypa/pip/pull/1053 for more details

References:

https://github.com/pypa/pip/issues/200

http://www.pip-installer.org/docs/pip/en/0.8.3/news.html#id4