Acidosis reprograms cancer cell metabolism to save fuel and energy. Lung cancer cells were incubated in medium containing 10 mM glucose with pH 6.8 or 7.4 and evaluated for bioenergetic metabolism. (A) Intracellular ATP contents and the ADP/ATP ratio. (B) The rates of cellular glucose consumption and lactate production. (C) A proportional fraction of ATP output from glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) and fuel dependency and capacity in OXPHOS. (D) Cellular oxygen consumption rate (OCR) and proton production rate (PPR). Combined measurements of OCR and PPR can provide metabolic phenotypes of cells as aerobic (high OCR and low PPR), energetic (high OCR and high PPR), glycolytic (low OCR and high PPR), or quiescent (low OCR and low PPR). (E) Cellular activities of rRNA synthesis determined by in situ nuclear run-on assay and (F) protein synthesis determined by surface sensing of translation (SUnSET) assay. (G) The total ATP consumption rate and proportional fraction of ATP expenditure. (F) Graphical summary of bioenergetic changes induced by acidosis. ∗P < 0.05 and ∗∗P < 0.01 by two-tailed unpaired t tests (n = 3–8). PPR, proton production rate; FCCP, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone; R/A, rotenone and antimycin A; FUrd, fluorouridine.