The digestive fluid of tropical pitcher plants (Nepenthaceae: Nepenthes L.) typically harbor communities of symbiotic organisms in nature, an example of a phytotelm ecosystem. While the inhabitants of pitchers (primarily the arthropods) have been described and studied from a community ecology perspective for over a century, many abiotic properties of the fluid environment have not been thoroughly documented. As the abiotic properties of the pitcher fluid micro-environment may have fitness and/or functional consequences on the inhabitants, it is of interest to examine intra and interspecific variation in fluid properties. Here I report observations of dissolved oxygen levels in Nepenthes pitchers. I find evidence that Nepenthes pitchers actively modify dissolved oxygen levels in the fluid and that this oxygenation ability may vary ontogenetically, with relatively hypoxic conditions in newly opened pitchers and high oxygen levels maintained in more mature pitchers.