Most essential oils will last for a month in the Electra-Essence Plug-In Diffuser. The following oils have a faster diffusion rate, below is an approximate time frame :

White camphor                                              123 hours                                                                5.125 days
Eucalyptus globulus                                        163 hours                                                                6.79 days
Bitter orange                                                  209 hours                                                                8.70 days
Blood orange                                                 209 hours                                                                8.70 days
Wild sweet orange                                         243 hours                                                                10.125 days
Mandarin                                                       243 hours                                                                10.125 days
Tangerine                                                      312 hours                                                                 13 days
Lemon                                                          333 hours                                                                 13.875 days
Rosemary                                                     432 hours                                                                 18 days
Eucalyptus smithii                                          456 hours                                                                 19 days
Spike lavender                                              504 hours                                                                 21 days
Eucalyptus radiata                                         552 hours                                                                 23 days
Niaouli cineole                                              576 hours                                                                 24 days
Wintergreen                                                  600 hours                                                                 25 days
Fir, Siberian                                                  672 hours                                                                 28 days