Shares in Royal Dutch Shell (LSE: RDSB) (NYSE: RDS-B.US) slipped by more than £1, over 4%, in early trade this morning, following the oil major's second-quarter and half-time results. Earnings on a current cost of supplies basis fell 20% to $4.6bn, compared to $5.7bn in the comparative quarter last year. Rising costs also contributed to the lower-than-expected figures, with crude oil, natural gas, oil products and chemicals all susceptible to fluctuating prices, while the company also highlighted increased exploration well write-offs as a contributor to the decline in earnings. Management pointed towards an identified net charge of $2.2bn for the sharp decline, "predominantly related to liquids-rich shales properties in North America". Additionally, Shell also took a hit of $700m for oil theft and gas supply disruptions in Nigeria and to cope with the impact of the weakening Australian dollar on a deferred tax liability.